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ICD-O-3 Guidelines
The revised 2026 Guidelines for ICD-O-3.2 Histology Code and Behavior Update
for cases diagnosed 1/1/2026 forward are now available on the NAACCR website. The update includes links to tables listing new terminology.
Please refer to the ICD-O-3 Archive
for older reference documents.
The NAACCR ICD-O-3 Implementation Work Group highly recommends all users read the guidelines which contain important coding information related to the 2026 update.
ICD-O-3 SEER Site/Histology Validation Lists
The Site/Histology List is not intended to be used for case finding or to determine reportability.
The ICD-O-3 Site/Type Validation program was modified to only allow for the site/histology/behavior combinations listed in this publication. All other cases must be reviewed.
- ICD-O-3 SEER Site/Histology Validation List (4/29/2022) implemented in January 2023 for cases diagnosed in 2023: PDF (PDF, 680 KB) or Excel (XLSX, 442 KB)
- 4/25/2023 Errata (PDF, 115 KB)
- 4/29/2022 Errata (PDF, 112 KB)
- 6/11/2021 Errata (PDF, 172 KB)
- 6/29/2020 Errata (PDF, 459 KB)
Refer to the ICD-O-3 Archive for older reference documents.
PLEASE NOTE: An ICD-O-3 SEER Site/Histology Validation List dated 4/25/2023 was posted to this site with associated Errata. The PDF and Excel files for the ICD-O-3 SEER Site/Histology Validation List dated 4/25/2023 have since been removed from this site. If you downloaded the ICD-O-3 SEER Site/Histology Validation List previously posted on 4/25/2023, please discard the file. For cases diagnosed as of January 1, 2024, the 2024 ICD-O-3 Cancer PathCHART Site-Morphology Validation List, released by the Cancer Pathology Coding Histology And Registration Terminology (Cancer PathCHART) initiative, has replaced the ICD-O-3 SEER Site/Histology Validation List as the definitive standard for the validity of tumor site-morphology code combinations.
The International Agency for Research on Cancer (IARC) provides an electronic version of ICD-O-3 on their website. However, the IARC versions are not identical to the versions used in the U.S. See the ICD-O-3 errata on this website and the NAACCR ICD-O-3 implementation guidelines for U.S. instructions.
