ObjectiveTo quantify the incidence of uterine leiomyoma confirmed by hysterectomy, ultrasound, or pelvic examination according to age and race among premenopausal women.MethodsFrom September 1989 through May 1993, 95, 061 premenopausal nurses age 25–44 with intact uteri and no history of uterine leiomyoma were followed to determine incidence rates of uterine leiomyoma. The self-reported diagnosis was confirmed in 93% of the medical records obtained for a sample of cases. Using pooled logistic regression, we estimated relative risks (RRs) of uterine leiomyoma according to race and examined whether adjustment for other potential risk factors could explain the variation in the race-specific rates.ResultsDuring 327,065 women-years, 4181 new cases of uterine leiomyoma were reported. The incidence rates increased with age, and the age-standardized rates of ultrasound-or hysterectomy-confirmed diagnoses per 1000 woman-years were 8.9 among white women and 30.6 among black women. After further adjustment for marital status, body mass index, age at first birth, years since last birth, history of infertility, age at first oral contraceptive use, and current alcohol consumption, the rates among black women were significantly greater for diagnoses confirmed by ultrasound or hysterectomy (RR 3.25; 95% confidence interval [CI] 2.71, compared with rates among white women. Women. We observed similar RRs when the cohort was restricted to participants who reported undergoing a screening physical examination within the 2 years before baseline.ConclusionA higher prevalence of known risk factors did not explain the excess rate of uterine leiomyoma among premenopausal black women.