OBJECTIVE To determine long-term efficacy of intravesical mitomycin C (MMC) versus bacille Calmette-Guérin (BCG) in patients with superficial bladder cancer with regard to recurrences and progression. METHODS Patients with superficial bladder cancer (pTa, pT1, pTis) were treated with intravesical MMC (30 mg, weekly for 4 weeks, and thereafter monthly for 5 months) or BCG (weekly for 6 weeks). RESULTS Three hundred forty-four patients were eligible (171 in the BCG group, 173 in the MMC group). The median follow-up was 7.2 years. Toxicity was not significantly different between the two treatment groups. Efficacy of the two treatment policies was similar with regard to tumor recurrence. With regard to progression to invasive disease, MMC was more effective than BCG in patients without carcinoma in situ (CIS) (P = 0.006). CONCLUSIONS We can confirm the conclusions of other studies that intravesical treatment with 30 mg of MMC remains an effective treatment option that can also be used in high-risk patients. Like others, we could not confirm that a 6-week course of BCG is more effective in the prevention of tumor progression. Of the 33 patients with tumor progression after intravesical therapy, 20 died of bladder cancer, confirming that tumor progression after intravesical therapy carries a poor prognosis. In this study the difference in toxicity between BCG and MMC was not significant. When comparing studies with MMC and BCG, differences in treatment schedule and/or patient selection should be kept in mind.