To assess the frequency of hospital encoded diagnoses of acute rheumatic fever (ARF) and Kawasaki disease (KD), the two leading causes of acquired heart disease in children in the United States, we performed a survey of the medical record departments of United States children's hospitals and of general hospitals that have at least 400 beds and a pediatric ward. With a simple questionnaire, data were gathered for the years 1984 through 1990 by ICD.9CM codes, with a 58% response rate. About 8000 diagnoses of KD and 6000 diagnoses of ARF were encoded during the study period. Encoded diagnoses of both KD and ARF showed yearly fluctuations in the earlier years (1984 through 1987). For KD there was a general trend toward increasing numbers after 1986. These data are consistent with increased physician awareness and diagnosis of KD. For ARF a gradual decline was observed between 1986 and 1990. About 80% of ARF diagnoses were reported from general hospitals. The much smaller pool of encoded diagnoses of ARF at the children's hospitals showed a 56% increase from 1985 to 1986. These data suggest that the highly publicized increase in cases of acute rheumatic fever in the United States during the mid-1980s may reflect focal rather than nationwide increased activity and that nationally the number of diagnoses of ARF actually may have continued to decline gradually from 1984 through 1990.