The prevalence of coronary heart disease (CHD) was determined in a general population sample of 9141 Icelandic men aged 34-79 years, and the prevalence of four different forms of CHD was estimated separately: symptomatic infarction fulfilling WHO-MONICA criteria for definite myocardial infarction; myocardial infarction detected by ECG changes only (unrecognized, silent infarction); angina pectoris detected by the Rose questionnaire and associated with ECG manifestations of myocardial ischaemia, either at rest or during exercise, but no manifestations of myocardial infarction; angina pectoris without ECG changes indicative of myocardial ischaemia. The study was conducted in five stages allowing evaluation of trends from 1968-1986. Age was a major determinant of the prevalence of all forms of CHD. Thus, the prevalence of myocardial infarction (symptomatic or silent) rose from undetectable levels in the youngest age group (30-34 years) to around 12% (7% symptomatic and 5% silent) in the oldest group (75-79 years) and the prevalence of all forms of CHD rose from 4% in the youngest age group to 23% in the age group 70-74 years. Age-standardized comparison was carried out on the prevalence of the different forms of CHD at different stages of the study in 50-64-year-old men who were represented in all stages of the study. There was a gradual increase in the prevalence of myocardial infarction from 3% (symptomatic and silent combined, CI 1.9-4.8) in 1968 to 4.9% in 1986 (CI 3.9-6.1) (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)