We evaluated prospectively the association between body mass index (BMI), height, recreational physical activity and the risk of bladder cancer among US adults. Data were used from 2 ongoing cohorts, the Health Professionals Follow-up Study and the Nurses' Health Study, with 3,542,012 years of follow-up and 866 incident bladder cancer cases (men = 507; women = 359) for the anthropometric analysis and 1,890,476 years of follow-up and 706 incident bladder cancer cases (men = 502; women = 204) for the physical activity analysis. Cox proportional hazard models were used to estimate incidence rate ratios (RR) and 95% confidence intervals (CI) between BMI, height, physical activity and bladder cancer risk adjusting for age, pack-years of cigarette smoking and current smoking. Estimates from each cohort were pooled using a random-effects model. We observed no association between baseline BMI and bladder cancer risk, even when we compared a BMI of > or =30 kg/m(2) to a BMI of 18-22.9 kg/m(2) [pooled multivariate (MV) RR, 1.16; 95% CI: 0.89-1.52]. A weak, but statistically significant, association was observed for the same comparison after excluding bladder cancer cases diagnosed within the first 4 years of follow-up (pooled MV RR, 1.33; 95% CI: 1.01-1.76). Height was not related to bladder cancer risk (pooled MV RR, 0.82; 95% CI: 0.65-1.03, top vs. bottom quintile). Total recreational physical activity also was not associated with the risk of bladder cancer (pooled MV RR, 0.97; 95% CI: 0.77-1.24, top vs. bottom quintile). Our findings do not support a role for BMI, height or physical activity in bladder carcinogenesis.