Gender and cigarette smoking are among the most consistent predictors of bladder cancer risk. After adjustment for known risk factors, an excess risk remains for males, suggesting that other factors may be responsible for the gender differences. Given limited data on hormonal or reproductive factors and bladder cancer risk, the authors examined these factors among women in the US Nurses' Health Study cohort. During 26 years of follow-up (1976-2002), 336 incident cases of bladder cancer were diagnosed. Cox proportional hazards models were used to estimate incidence rate ratios and 95% confidence intervals between hormonal and reproductive factors and bladder cancer risk. Postmenopausal women, compared with premenopausal women, were at increased risk (incidence rate ratio = 1.93, 95% confidence interval: 0.99, 3.78). For postmenopausal women, early age at menopause (</=45 years) compared with late age at menopause (>/=50 years) was associated with a statistically significant increased risk of bladder cancer (incidence rate ratio = 1.63, 95% confidence interval: 1.20, 2.23). The association between age at menopause and bladder cancer risk was modified by cigarette smoking status (p for interaction = 0.01). The authors observed no significant associations of age at menarche, parity, age at first birth, and exogenous hormone use with bladder cancer risk. Findings suggest that menopausal status and age at menopause may play a role in modifying bladder cancer risk among women.