This cohort study aimed to investigate prognostic significance of plasma folate and cobalamin in non-muscle-invasive bladder cancer (NMIBC). A total of 177 NMIBC patients were followed over a period extending to 6 years. Cox regression models were applied to estimate risks for recurrence and progression according to plasma vitamins tertiles. Compared to first tertile, third tertile of plasma folate [HR (95% CI), 10.5 (1.32–83.4); p = 0.026] was associated, and of plasma cobalamin [2.12 (0.63–7.25); p = 0.116] tended to be associated with higher risk for progression. NIMBC patients with high folate/cobalamin statuses should make the physician more alert for a likely poor outcome. [ABSTRACT FROM AUTHOR]