Objective: The present study evaluated the long-term results of intravesical mitomycin C (MMC) instillation after transurethral resection (TUR) in 242 consecutive patients with superficial bladder cancer at high risk of recurrence (stage Ta, grade 1–3, or stage T1, grade 1 and 2, primary multiple or recurrent tumor). Materials and Methods: 242 patients were treated with weekly instillations of 40 mg MMC for 8 weeks after TUR. Tumor-free patients then followed a maintenance course with monthly instillations for 3 months. Results: Median follow-up of disease-free patients is 43.5 (range 23–112) months. The incidence of first recurrence is 59.5% (144/242 patients) with a median time to first recurrence of 29 months. 95 patients (39.3%) remained disease-free. Three had disease progression as the first event. The risk of recurrence was significantly higher for multifocal tumors (p = 0.0023, hazard ratio 1.79, 95% CI 1.23–2.59). Overall, patients have been followed for a median time of 57 (range 10–114) months. During this period the recurrence rate was 4.9. Eleven more patients had disease progression. The progression rate is 5.8% (14/242), with a mean time to progression of 34 months. At present 209 patients are alive, 6 have died of bladder cancer, 16 of causes unrelated to the disease and 11 (4.5%) have been lost to follow-up. Thus the crude survival rate is 86.4%, disease-specific mortality 2.5%, and non-disease-specific mortality 6.6%. Conclusions: Patients with multiple tumors seem to benefit the least from MMC instillation. Probably recurrent disease could be better prevented with intravesical bacillus Calmette-Guérin.