The incidence of acute rheumatic fever has varied over the past several decades. The usual source of case ascertainment has been medical record discharge diagnosis coding. By reviewing both the Children's Hospital of Pittsburgh medical records discharge data and the Division of Cardiology computer database for the years 1982 to 1993, 173 cases of acute rheumatic fever were identified including 63 patients who were managed exclusively as outpatients. Seventy-three percent of patients diagnosed before 1990 were managed as inpatients, compared with 48% of patients diagnosed 1990 and later. The incidence of acute rheumatic fever may be underestimated if patients managed without hospitalization are not identified.