Familial aggregation of coronary heart disease (CHD) and specific major risk factors were determined among 639 first-degree relatives of 73 women with confirmed coronary death before age 55. They were compared with 1,151 persons in 141 control families. Of women with early coronary death, 62% had first-degree relatives with early coronary disease compared with 12% of affected control family members. In the proband families, coronary incidence rates were 2.7 times the control population rates for women (P<.001) and 1.6 times the control population rates for men (P<.05). An excess incidence of coronary disease was observed for ages 45 to 74 in both men and women.Smoking, hypertension, diagnosed hyperlipidemia and diabetes were all two to three times more common in the female probands with early coronary death than in healthy controls. Hypertension was more common in all proband relatives (both sexes with and without coronary disease). Smoking was more common among female relatives of probands when compared with the controls. These data suggest that early coronary disease in women is often familial and associated with smoking and hypertension. The familial aggregation seems to be stronger in female relatives of female probands with early CHD than in male relatives. Genetic factors or shared family life-style or both likely account for these observations.