Abstrak: Clinical and experimental findings suggest that female hormonal and reproductive factors could influence kidney cancer development. To evaluate this association, we conducted analyses in 2 large prospective cohorts (the National Institutes of Health-AARP Diet and Health Study (NIH-AARP), 1995-2006, and the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial (PLCO), 1993-2010). Cohort-specific and aggregated hazard ratios and 95% confidence intervals relating reproductive factors and kidney cancer risk were computed by Cox regression. The analysis included 792 incident kidney cancer cases among 283,952 postmenopausal women. Women who had undergone a hysterectomy were at a significantly elevated kidney cancer risk in both NIH-AARP (hazard ratio = 1.28, 95% confidence interval: 1.09, 1.50) and PLCO (hazard ratio = 1.41, 95% confidence interval: 1.06, 1.88). Similar results were observed for both cohorts after analyses were restricted to women who had undergone a hysterectomy with or without an oophorectomy. For the NIH-AARP cohort, an inverse association was observed with increasing age at menarche (P for trend = 0.02) and increasing years of oral contraceptive use (P for trend = 0.02). No clear evidence of an association with parity or other reproductive factors was found. Our results suggest that hysterectomy is associated with increased risk of kidney cancer. The observed associations with age at menarche and oral contraceptive use warrant further investigation.