We studied the hospital records of 124 patients with a discharge diagnosis of acute rheumatic fever who were hospitalized in 21 Minneapolis-St. Paul hospitals during 1975 and 1976. After careful review of the hospital records, we found that 83 (67 per cent) of these patients did not have an acute illness. Seventeen (41 per cent) of the 41 cases with an acute illness were thought to adequately fulfill the Jones' Criteria for acute rheumatic fever. Upon review of the rheumatic fever registry of the Minnesota State Health Department, we found that less than one-half of the hospitalized patients had been reported to the registry. Cases that fulfilled and did not fulfill the Jones' Criteria were reported with equal frequency, indicating significant underreporting and overreporting of rheumatic fever. Evaluation of secondary rheumatic fever prophylaxis, both in those patients with acute rheumatic fever as well as in those with rheumatic heart disease, indicated that many patients who, in theory, should be receiving prophylaxis were not receiving it. These studies indicate a need for more thorough evaluation of the current epidemiology of rheumatic fever and the role of a rheumatic fever registry, and imply a need for reevaluation of these programs. (Am J Public Health 69:767-771, 1979).