An ad hoc committee of the North American Primary Care Research Group (NAPCRG) was appointed to adapt the diagnosis clusters instrument for use with the International Classification of Diseases (ICD-9-CM) and the International Classification of Health Problems in Primary Care (ICHPPC-2). This article describes the development and testing of the final roster of 110 diagnosis clusters for family physicians. Almost 90 percent of all diagnoses recorded by family physicians in a variety of settings were included in the clusters. The diagnosis clusters can be used in the analysis of large databases and facilitate comparisons between different providers and practices.