Diagnosis Code Set General Equivalence Mappings
ICD-10-CM to ICD-9-CM and ICD-9-CM to ICD-10-CM
2012 Version
Documentation and User’s Guide

The information furnished here accompanies the 2012 release of the National Center for Health Statistics (NCHS) public domain diagnosis code reference mappings of the International Classification of Diseases 10th Revision Clinical Modification (ICD-10-CM) and the International Classification of Diseases 9th Revision (ICD-9-CM) Volumes 1 & 2. The purpose of this website is to give readers the information they need to understand the structure and relationships contained in the mappings so they can use the information correctly. The intended audience includes but is not limited to professionals working in health information, medical research and informatics. General interest readers may find section 1 useful. Those who may benefit from the material in both sections 1 and 2 include clinical and health information professionals who plan to directly use the mappings in their work. Software engineers and IT professionals interested in the details of the file format will find this information in Appendix A.

The network of relationships between the two code sets described herein is named the General Equivalence Mappings (GEMs).

  • Section 1 is a general interest discussion of mapping as it pertains to the GEMs. It includes a discussion of the difficulties inherent in translating between two coding systems. The specific conventions and terms employed in the GEMs are discussed in more detail.
  • Section 2 contains detailed information on how to use the GEM files for users who will be working directly with applied mappings now or in the future—as coding experts, researchers, claims processing personnel, software developers, etc.
  • The Glossary provides a reference list of the terms and conventions used—some unique to this document—with their accompanying definitions.
  • Appendix A contains tables describing the technical details of the file formats, one for each of the two GEM files:
    1. ICD-9-CM to ICD-10-CM (I-9 to I-10)
    2. ICD-10-CM to ICD-9-CM (I-10 to I-9)