Among 121,964 women aged 30-55 years in 1976, 117,156 who were initially free from coronary heart disease provided information on a number of coronary risk factors including parental history of myocardial infarction and were followed prospectively. In 1976, 31,101 (26.5%) reported that at least one parent had suffered a myocardial infarction. Questionnaires in 1978 and 1980 identified women who had developed nonfatal myocardial infarction (n = 132) and angina pectoris (n = 101). Fatal coronary heart disease cases (n = 42) were ascertained by searches of state vital records. The age-adjusted relative risk of nonfatal myocardial infarction for women with a parental history of myocardial infarction less than or equal to 60 years of age compared with women with no family history was 2.8 (95% confidence limits (CL) 1.8, 4.3). For those with a parental history of myocardial infarction greater than 60 years of age, the age-adjusted relative risk of nonfatal myocardial infarction was 1.0 (CL 0.5, 1.8). The age-adjusted relative risks of fatal coronary heart disease were 5.0 (CL 2.7, 9.2) for parental history before age 61 and 2.6 (CL 1.1, 5.8) for parental history after age 60. The corresponding relative risks of angina pectoris were 3.4 (CL 2.2, 5.2) and 1.9 (CL 1.2, 3.2), respectively. These associations were only slightly altered by adjustment for history of hypertension, diabetes, high cholesterol, use of oral contraceptives, menopause, postmenopausal hormone use, obesity, or smoking, in individual stratified analysis or in multivariate analyses. These data support the hypothesis that parental history of myocardial infarction has an independent effect on risk that is not explained solely by individual risk factors.