Obesity has been linked to various malignancies, but a clear relation of overweight with urothelial cancer has not been established. We assessed the association between adolescent obesity and future risk for urothelial cancer. Medical data on 1,110,835 Israeli adolescents examined for fitness for military duty between 1967 and 2005 were linked to the National Cancer Registry in this nationwide population-based cohort study. We used Cox proportional hazards modeling to estimate the covariate-adjusted hazard ratio (HR) for urothelial cancer associated with BMI measured at age 17. The mean follow-up of 17.6 ± 10.8 years reflected 19,576,635 person years, during which 661 examinees developed urothelial cancer of the bladder, ureter, or renal pelvis. BMI 85th standard percentile in adolescence significantly predicted increased risk of urothelial cancer with a HR (adjusted for year of birth, education and religiosity) of 1.42 (95% confidence interval (CI), 1.13-1.77, P = 0.002). Similar results were observed using the 25 kg/m 2 definition of overweight (HR = 1.36 (95% CI, 1.08-1.72), P = 0.008). Incidence of urothelial cancer was significantly lower in the more educated and among those who attended religious schools. Overweight in adolescence is related to increased risk of future urothelial cancer. In view of the growing incidence of both urothelial cancer and adolescent obesity, our study suggests an avenue for possible prevention of urothelial cancer.