Object: We aimed to analyze the risk of kidney and bladder cancer according to the baseline duration of diabetes mellitus (DM) in a longitudinal nationwide cohort. Methods: This study was conducted in a cohort of 9,773,462 participants ≥20 years old who underwent a National Health Examination in 2009 and were followed up until December 2017. The primary outcome was newly diagnosed kidney or bladder cancers, which was defined as C64 and C67 according to the ICD-10. Results: During follow-up (mean 7.3 years), kidney and bladder cancer occurred in 11,219 and 13,769 participants. DM was associated with an increased risk of kidney and bladder cancer (hazard ratio (HR), 95% confidence interval (95% CI); 1.14, 1.09-1.20 and 1.23, 1.17-1.28, respectively). Compared to fasting glucose <100 mg/dL, prediabetes and longer DM duration were associated with increased risks (HR, 95% CI): impaired fasting glucose (1.05, 1.01-1.10), new-onset DM (1.13, 1.03-1.24), DM < 5 years (1.11, 1.02-1.20), and DM ≥ 5 years (1.25, 1.15-1.36) in kidney cancer; IFG (1.05, 1.01-1.09), new-onset DM (1.10, 1.01-1.19), DM < 5 years (1.26, 1.18-1.35), and DM ≥ 5 years (1.34, 1.26-1.43) in bladder cancer, respectively. Conclusion: Our findings suggest that the subjects with prediabetes and longer duration of diabetes had a higher risk for both kidney and bladder cancer than those without diabetes.