A communitywide study was conducted in all 16 acute general hospitals in the metropolitan Worcester, Mass, area during the calendar years 1975, 1978, and 1981 to examine time trends in the attack and case-fatality rates of patients hospitalized with validated acute myocardial infarction as well as of the occurrence of out-of-hospital coronary heart disease (CHD) deaths. Between 1975 and 1981, there was an increase in the age-adjusted attack rates of initial events of acute myocardial infarction (1975, 254/100,000; 1981, 280/100,000) as well as recurrent events (1975, 133/100,000; 1981, 156/100,000). These overall increases were due to an increase among those 65 years of age and older, with no significant changes observed in those less than 65 years old. The age-adjusted in-hospital case-fatality rates declined from 22.1% in 1975 to 20.3% in 1978 and 17.4% in 1981. In examining long-term prognosis, no significant differences were seen over an eight-year follow-up period between patients discharged in 1975, 1978, and 1981. The age-adjusted mortality rates of out-of-hospital CHD deaths significantly declined between 1975 (229/100,000) and 1981 (147/100,000). The results of this population-based survey suggest that recently observed declines in the mortality rates of CHD may reflect decreases in out-of-hospital coronary deaths and improving trends in the in-hospital survival of patients with acute myocardial infarction.