We examined the association of reproductive and hormonal factors with renal cell cancer risk in a cohort study of 89 835 Canadian women. Compared with nulliparous women, parous women were at increased risk (hazard ratio (HR) 1.78, 95% confidence interval (CI) 1.02-3.09), and there was a significant gradient of risk with increasing levels of parity: relative to nulliparous women, women who had > or =5 pregnancies lasting 4 months or more had a 2.4-fold risk (HR=2.41, 95% CI=1.27-4.59, P for trend 0.01). Ever use of oral contraceptives was associated with a modest reduction in risk. No associations were observed for age at first live birth or use of hormone replacement therapy. The present study provides evidence that high parity may be associated with increased risk of renal cell cancer, and that oral contraceptive use may be associated with reduced risk.