To evaluate the risk factors for coronary disease, 345 women, aged 35 to 59 years, who had undergone coronary arteriography for suspected coronary disease completed a mail questionnaire, telephone interview, or both. Two hundred eight women with angiographically normal coronary arteries constituted the control group, and 137 with a 70% or more occlusion of one or more coronary vessels were classified as having severe coronary occlusive disease. Age-adjusted odds of severe coronary disease based on the logistic regression model for the risk factors evaluated were as follows: smoking, 5.73 (p less than 0.001); diabetes, 5.09 (p less than 0.001); cholesterol level greater than 240 mg/dl, 2.35 (p less than 0.05); a parental history of death from heart disease before age 60 years, 2.03 (p less than 0.05); and estrogen use for 6 months or longer, 0.50 (p less than 0.01). There were no differences with regard to the presence of obesity and a history of hypertension in women with and without coronary disease. These data support the hypothesis that use of noncontraceptive estrogen significantly reduces the risk of severe coronary disease, whereas smoking, an elevated cholesterol level, and a parental history of heart disease all increase the risk of ischemic heart disease in women.