Table Of Contents

Introduction

Background

SNOMED CT provides a common language that enables a consistent way of indexing, storing, retrieving, and aggregating clinical data across specialties and sites of care.

SNOMED International maintains the SNOMED CT technical design, the content architecture, the SNOMED CT content (includes the concepts table, the descriptions table, the relationships table, a history table, and ICD mappings), and related technical documentation.

Purpose

This document provides a summarized description of the content changes included in the May 2026 release of SNOMED Clinical Terms^® (SCT) International Edition.

It also includes notes detailing the known content or technical issues where the root cause is understood, the fix has been discussed and agreed to, but has yet to be implemented.

The SNOMED International release notes are available alongside the May 2026 International Edition.

Scope

This document is written for the purpose described above and is not intended to provide details of the technical specifications for SNOMED CT or encompass every change made.

Audience

The audience includes National Release Centers, WHO-FIC release centers, vendors of electronic health records, terminology developers and managers who wish to have an understanding of changes that have been incorporated into the May 2026 International Edition.

Please note, you may have to register for a user account in order to access the links included in these release notes.

Content Development Activity

Summary

Continuous quality improvement and enhancement of existing content is an ongoing process undertaken by SNOMED International in preparation for every release. The May 2026 International Edition has seen a continuation of the work driven by contributions from: Kaiser Permanente i.e. Convergent Medical Terminology (CMT), Global Medical Device Nomenclature Agency (GMDNA), Orphanet and other domain specific collaborations as well as requests received via the Content Request System (CRS). 

Additionally quality improvement activities are advanced via project driven initiatives summarized below.  Additional work items impacting every release are updates to the SNOMED CT derived maps such as ICD-10 and ICD-O; details are included in these release notes.  

Information about editorial decisions may be found in the SNOMED CT Editorial Guide; mapping guidance for ICD-10 can be found here.

Quality Assurance

Update Historical Association WAS_A

224 concepts previously inactivated using the WAS_A inactivation reason have been reviewed. The inactivation reason was changed to one of the current allowed reasons and the historical association value was also updated where needed.

Update Hierarchy 414916001 |Obesity (disorder)|

Modeling updates have been made to obesity and central obesity concepts to better reflect that obesity is defined by excess adiposity, rather than body weight alone. As part of this work, obesity concepts have been remodeled using body fat, central obesity has been remodeled using distribution of body fat, and 840358001 |High body weight (finding)| has been inactivated with reason ambiguous.

Synonym updates have also been made to support clearer representation of central and android obesity.

Number of concepts edited (approx): 90

Body Structure 

New Content - Wall of Tracheobronchial Tree

Enhancement has been made to the coverage for ‘wall of tracheobronchial tree’ with the addition of new concepts:

• Wall of tracheobronchial tree

• Wall of bronchus

• Wall of bronchiole

• Wall of trachea

• Lumen of bronchiole

The existing structures, such as mucosal membrane, muscle, and cartilage of walls have been reorganized.

Number of concepts edited (approx): 30

New Content - Inner Boundary Line of Lips

New concepts for the inner boundary line of lips (Structure of border of vermilion and mucosa of lip) have been added and the FSNs of the existing concepts of the outer boundary line have been updated to 'Structure of border of vermilion and skin' to clarify the meaning and avoid confusion.

Number of concepts edited (approx): 12

SEP and Laterality Anatomy Reference Sets

The release file for the lateralizable body structure reference set has been updated and validated.

The release file for the SEP reference set has been updated and validated.

Clinical Finding

Update Hierarchy 233703007|Interstitial lung disease (disorder)|

New concepts have been added to align with the 2025 update of the International Multidisciplinary Classification of the Interstitial Pneumonias. The new concepts have attribution to ERS/ATS - European Respiratory Society/American Thoracic Society.

For these new concepts, the fully specified name and preferred term have been added to align with the classification which uses the term ‘pneumonia’ instead of ‘pneumonitis’ even in the absence of an infectious cause. These new concepts are an exception to existing guidance here.

Update Hierarchy 239862000 |Primary osteoarthritis (disorder)|

A new concept, 1389261008 |Primary generalized osteoarthritis (disorder)| has been added.

239862000 |Idiopathic osteoarthritis (disorder)| has been updated to 239862000 |Primary osteoarthritis (disorder)|. Idiopathic osteoarthritis was retained as a synonym.

The primary generalized OA synonyms on 239862000 |Primary osteoarthritis (disorder)| have been inactivated as duplicates of 1389261008 |Primary generalized osteoarthritis (disorder)|.

The existing concept 201829007 |Localized, primary osteoarthritis (disorder)| has been updated to become sufficiently defined and the subtypes (primary, localized) osteoarthritis concepts have also been remodeled to align with the Editorial Guide.

Seven primary osteoarthritis concepts have been updated to the proximal primitive parent 239862000 |Primary osteoarthritis (disorder)| to become sufficiently defined.

201841000 |Primary gonarthrosis, bilateral (disorder)| has been inactivated as a duplicate of 607861000202103 |Primary osteoarthritis of bilateral knee joints (disorder)|.

A new concept 1389445009 |Structure of joint of midfoot (body structure)| has been added and appropriate subtypes assigned.

Number of concepts edited (approx): 20

Medicinal Product

Update Language Acceptability for Sulfate/Sulphate

A recent change to the language reference sets has resulted in new 429 warnings. The word sulfate has a GB alternative of sulphate. Sulphate with the 'ph' spelling is the GB acceptable synonym (not acceptable US) for concepts with sulfate in the description.

A bulk change will be made to the concepts impacted, in the meantime the 429 warnings have been added to the temporary exception list.

Organism

Update Hierarchy 112277009 |Genus Borrelia (organism)|

A new concept for genus Borreliella has been added. Current subtypes of 112277009 |Genus Borrelia (organism)| have been reviewed. Subtypes have been renamed and reassigned to the newly added genus Borreliella, where appropriate. Genus Borreliella has the additional descriptions of 'Lyme disease Borrelia' and 'Borrelia burgdorferi sensu lato complex’. Descriptions of impacted clinical finding concepts have also been updated.

Collaboration/Harmonization Agreements

Convergent Medical Terminology (CMT)

153 new CMT disorder concepts have been added for the May 2026 release with a key focus on fractures and injuries together with a small number of other disorder concepts.

Orphanet

Working in collaboration with Orphanet efforts are ongoing to update rare disease concepts in SNOMED CT to maintain alignment with Orphanet for the annual update of the SNOMED CT to Orphanet Maps. This map is at disorder level. In scope content has been annotated with attribution to Inserm Orphanet.

All of the concepts added for the Orphanet project have been mapped to ICD-10.

International League Against Epilepsy (ILAE)

In line with approved harmonized terminology, this project is working on alignment including restructuring to update the hierarchy  << 313307000 |Epileptic seizure (finding)|.

Further information about this collaboration is available here.

Internal Quality Improvement

Machine Readable Concept Model (MRCM) Changes

The following changes have been made for the MRCM in the May 2026 International Edition.

• Update MRCM attribute cardinality of 370134009 |Time aspect (attribute)| - the attribute cardinality of 370134009 |Time aspect (attribute)| has been updated from 0..1 to 0..* for evaluation procedures. This change has been made to support multiple properties in concept modeling. This is aligned with the cardinality for observables. 

• Update MRCM attribute cardinality of 370130000 |Property (attribute)| - the attribute cardinality of 370130000 |Property (attribute)| has been updated from 0..1 to 0..* for evaluation procedures. This change has been made to support multiple properties for the concept model, e.g. 624521000052106 |Plain X-ray of bilateral lower limbs for bone length measurement (procedure)|. 

• New MRCM Attribute 129453003 |Has deficiency of (attribute)| - new MRCM for the existing attribute `129453003 |Deficiency of (attribute)|` to support the modeling of physiological disorders.

• New MRCM Attribute 1395997003 |Has excess of (attribute)| - new MRCM for the attribute `1395997003 |Has excess of (attribute)|` to support the modeling of physiological disorders. 

• New MRCM Attribute HAS ASSOCIATED GENE - new MRCM for attribute 1395996007 |Has associated gene (attribute)| to support modeling of genetic disorders.

Future changes that are currently in progress can be viewed via the MRCM Daily Build Browser

Please see Early Visibility Release Notifications for future planned changes to MRCM.

Annotation Reference Set

The addition of content for the Annotations refset was commenced in the July 2024 International Edition release and is ongoing for attribution of in scope content that is part of a collaboration agreement. Where content with attribution no longer falls into scope for a collaboration agreement, the attribution has been inactivated.

SNOMED CT derived products

SNOMED CT - ICD-10 map

The SNOMED CT to the International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (© World Health Organization 1994) 2016 Version map (SNOMED CT to ICD-10 Map) is included in the SNOMED CT International Edition as a Baseline. The SNOMED CT to ICD-10 Map was created to support the epidemiological, statistical and administrative reporting needs of SNOMED International member countries and WHO Collaborating Centers.

The SNOMED CT to ICD-10 Map is released in Release Format 2 (RF2) only. It is located in the file der2_iisssccRefset_ExtendedMapFull_INT_20200731.txt, which is in the Map folder under Refset, in each of the three RF2 Release Type folders. 

The SNOMED CT to ICD-10 Map is released as Refset 447562003 |SNOMED CT to ICD-10 extended map (foundation metadata concept).

The ICD-10 Mapping Technical Guide (including exemplars) is here.

Content Development Activity Summary

The map is a directed set of relationships from SNOMED CT source concepts to ICD-10 target classification codes.  The SNOMED CT source domains for the map are constrained to subtypes of 404684003 |Clinical finding (finding)|, 272379006 |Event (event)|, and 243796009 |Situation with explicit context (situation)|. The target classification used is the ICD-10 WHO version 2016 (https://icd.who.int/browse10/2016/en#/).

The map provided for this release has been updated and represents a complete map from the May 2026 release of the SNOMED CT International Edition to the ICD-10 WHO version 2016.

This includes:

Mapped content for May 2026 release

• Addition of 399 new mapped concepts (includes 2 reactivations)

• Updates to 143 existing mapped concepts

• Retirement of 30 mapped concepts

The SNOMED CT to ICD-O morphology map has zero content changes for this release.

We welcome feedback on any issues that users may detect when deploying the map. Issues can be reported to mapping@snomed.org.

SNOMED CT to OWL conversion and classification

The repository containing the toolkit enabling simple SNOMED CT to OWL conversion and classification can be found here, including documentation on its use: https://github.com/IHTSDO/snomed-owl-toolkit

Please contact SNOMED International at support@snomed.org if you would like to provide any feedback on ways to extend and improve the new toolkit.

Technical notes

Known Issues

Known Issues are content or technical issues where the root cause is understood, and the resolution has been discussed and agreed but has yet to be implemented.  This can be due to a number of reasons, from lack of time within the new monthly editing cycles, to the risk of impact to the stability of SNOMED CT if the fix were to be deployed at that stage in the Product lifecycle.  

For the current SNOMED CT International Edition, the following Known Issues were identified, and agreed to be resolved in future editing cycles:

Resolved Issues

Resolved issues are Known Issues which were not fixed as part of the previous release lifecycle, but which have now been resolved in the latest release.  They can also be issues found during testing of the current release, which were resolved before the final deployment of the Production release.  Finally they can be issues which were reported or found during the testing phase, but which have been closed without any action taken.  

The Resolved Issues for the current SNOMED CT International Edition can be found here:

Technical updates

RF2 package format

The RF2 package convention dictates that all relevant files are included, regardless of whether or not there is content to be included in each release.  Therefore, the package contains a mixture of files which contain both header rows and content data, and files that (intentionally) include only header records.  The reason that these "empty" files are included in the package is to draw a clear distinction between:

1. ...files that have been deprecated (and therefore removed from the package completely), due to the content no longer being relevant to RF2 in future releases 

2. ...files that happen to contain no data in this particular release (and are therefore included in the package with just a header record), but are still relevant to RF2, and could therefore contain content in future releases.

This allows users to easily distinguish between the two scenarios, as otherwise if files in option 2 were left out of the package it could be interpreted as an error, rather than an intentional lack of content in that release.

ADVANCED NOTICE: Deprecation of the CNC Indicators from the International Edition

Following on from the announcements in late 2024 and early 2025, the plan to deprecate the Concept Non Current Indicators from the International Edition release is as follows, and implementation was started in the January 2026 International Edition release:

ADVANCED NOTICE: Increase to the maximum length of Description Types

Please see here for the latest announcement on the plan to increase the limit of characters allowed in Descriptions.

A community consultation was completed to solicit feedback on the proposal to increase the size limits of SNOMED CT concept descriptions to 4096 from the current limit of 255 characters. While this change does not represent a modification of the existing specification, there is a potential for it to be disruptive to implementers who have coded fixed length limits into their systems.  

Please read the full proposal, along with the latest Q&A blog post for details of the planned changes, the potential benefits, and the issues that may need to be considered to prepare for the transition in 2026.

Early visibility of impending changes in Monthly International Edition releases

Please see the 2026 Early Visibility Notices for details of forthcoming changes.