The role of hormones in ischemic heart disease is of considerable interest, but limited data are available pertaining to risk factors associated with endogenous hormones. We examined the association between menstrual and reproductive factors and ischemic heart disease in a cohort of 867 white, college-educated women who prospectively recorded menstrual cycle-data for at least 5 years from their early 20s through their menopause. Ischemic heart disease history was obtained from a self-administered (N = 714) or proxy-administered (N = 153) questionnaire completed at a mean age of 73 years. The analysis included 44,899 person-years of follow-up and 45 cases of myocardial infarction, angioplasty, heart bypass surgery, or ischemic heart disease-related mortality. Ischemic heart disease risk decreased with increasing age at menarche (age-adjusted RR 0.76 per year, 95% CI = 0.60–0.95). Considering menstrual cycle characteristics ages 28–32, there was little overall association with length, variability, or bleeding duration. Ischemic heart disease risk increased with later age at first birth (age-adjusted RR 2.90 for ages 33–43 compared with 25–29) and later age at last birth (age-adjusted RR 3.79 for ages ≥40 compared with 35–39), but there was little association with high parity. (Epidemiology 1999;10:255–259)