The Medical Knowledge Self-Assessment Program of the American College of Physicians is one of the largest continuing medical education programs in the United States. The scope and educational rationale for each of the components of the program are described. More than 32 000 physicians used one or more components during 1977 and 1978. Performance on the self-assessment examinations showed that, on the average, participants who submitted answer sheets scored in the range of 65% to 75% correct responses. Participants performed better in areas reflecting their special interests and, in general, performance appeared to improve for groups that were closer to the completion of formal training in internal medicine. Specific suggestions have been made as to how the program might be improved in future years.