A collaboration between the International Health Terminology Standards Development Organisation (IHTSDO®) and the World Health Organization (WHO) has resulted in a priority set of cross maps from SNOMED CT^® to ICD-10^® to support the epidemiological, statistical and administrative reporting needs of the IHTSDO member countries, WHO Collaborating Centres, and other interested parties. Overseen by the Joint Advisory Group (JAG), approximately 20,000 SNOMED CT concepts have been mapped to ICD-10 using a stand-alone mapping tool. The IHTSDO Map Special Interest Group (MapSIG) developed the mapping heuristics and established the validation process in conjunction with the JAG. Mapping team personnel were selected and then required to participate in a training session using the heuristics and tool. Quality metrics were used to assess the training program. An independent validation of cross map content was conducted under the supervision of the American Health Information Management Association. Lessons learned are being incorporated into the plans to complete the mapping of the remaining SNOMED CT concepts to ICD-10.