This report documents the methods used to reclassify Army Medical Department (AMEDD) International Classification of Diseases, Ninth Revision (ICD-9) and International Classification of Procedures in Medicine (ICPM) data to International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM). This process required significant interaction with national nosology consultants and civilian universities. The purpose of the reclassification or conversion was to employ a recently developed diagnosis grouping method called Diagnosis Related Groups (DRGs). The AMEDD needed a more clinically relevant method of describing workload and developing meaningful length of stay data. This report describes the success of the reclassification effort as well as the application of DRGs to AMEDD performance. The study concludes that the conversion method is effective and that the data classified into DRGs is a substantial improvement over previous patient grouping methods employed within the AMEDD or by the Office of the Assistant Secretary of Defense for Health Affairs. Keywords: Disease classification, Diagnosis grouping, Diagnosis Related Groups, DRG, Crosswalk.