In etiologic studies of renal cell carcinoma the role of reproductive variables and the use of exogenous hormones have not been well examined. In a population-based case-control study including 165 female cases and 227 controls, we assessed the risk of renal cell cancer associated with reproductive factors and use of oral contraceptives and menopausal hormones. Odds ratios were computed using logistic regression analyses. Risk was positively associated with number of births and inversely associated with age at first birth, with the largest increases in risk (more than 2-fold) among women with 5 or more births after age 25. After adjustment for age, smoking status, body mass index and age at first birth, women with 5 or more births had a 2-fold risk (OR = 2.2, 95% CI = 1.2-4.0) relative to those with 1 or 2 births. Age at first birth, however, was no longer a risk factor when the number of births was adjusted for. The association with parity was considerably stronger among women with a history of hypertension or above-median body mass index than among those without these conditions. In addition, risk was reduced among long-term oral contraceptive users but elevated among women who had had a hysterectomy or used menopausal hormones. Our findings suggest that reproductive factors, particularly the number of births, may play an etiologic role in renal cell cancer among women and deserve further study.