Nonmuscle-invasive bladder cancer (NMIBC) has high recurrence rates and is often treated with mitomycin C (MMC) and bacillus Calmette-Guérin (BCG). Their efficacy relies on phase 2 enzyme metabolism and immune response activation, respectively. Dietary isothiocyanates, phytochemicals in cruciferous vegetables, are phase 2 enzyme inducers and immunomodulators, and may impact treatment outcomes. We investigated the modifying effects of cruciferous vegetable and isothiocyanate intake on recurrence risk following MMC or BCG treatment. Self-reported cruciferous vegetable intake, estimated isothiocyanate intake, and urinary isothiocyanate metabolites were collected from 1158 patients with incident NMIBC in the prospective Be-Well Study. Hazard ratios (HRs) and 95% CIs were calculated from Cox proportional hazards regression models for risk of first recurrences, and random effects Cox shared frailty models for multiple recurrences. Over median follow-up of 23 months, 343 (30%) recurrences occurred. Receipt of MMC and BCG was associated with decreased risks of first recurrence (MMC: HR = 0.58; 95% CI: 0.46-0.73; BCG: HR = 0.66; 95% CI: 0.49-0.88) and multiple recurrences (MMC: HR = 0.55; 95% CI: 0.44-0.68; BCG: HR = 0.72; 95% CI: 0.55-0.95). Patients receiving BCG and having high intake (>2.4 servings/mo), but not low intake, of raw cruciferous vegetables had reduced risk of recurrence (HR: 0.56; 95% CI: 0.36-0.86; P for interaction = .02) and multiple recurrences (HR: 0.51; 95% CI: 0.34-0.77; P for interaction < .001). The inverse association between MMC receipt and recurrence risk was not modified. For NMIBC patients who receive induction BCG, increasing consumption of raw cruciferous vegetables could be a promising strategy to attenuate recurrence risk.