Occurrence of coronary heart disease was assessed in families of 211 men under the age of 56 from East Finland. Fifty men were survivors of recent myocardial infarctions, 55 had died of myocardial infarction, 53 suffered from uncomplicated angina pectoris, and 53 were healthy reference men. Overall prevalence of coronary heart disease was similar in familes of all case probands. By age 70, case fathers had a 6 times greater cumulative risk (a 36% chance) of dying from coronary heart disease than reference fathers, whereas there was only a small difference between case and reference mothers. Cumulative risk of developing fatal or non-fatal coronary heart disease by age 65 was 4.5-fold for case brothers (70%) and 2.6-fold for case sisters (40%), when compared with reference sibs. The risk was greatest for case sibs with a parental, especially a maternal, history of premature coronary heart disease. Clinical manifestations of coronary heart disease showed similarities within sibships. Cardiac deaths were commonest in sibs of the fatal myocardial infarction probands, whereas angina was commonest in sibs of the angina pectoris probands.