The effectiveness of BCG in preventing disease progression in patients with superficial bladder cancer is evaluated. Long-term follow-up of high-risk patients treated in a previously reported randomized control trial of intravesical plus percutaneous BCG shows that progression occurred in 41/43 (95%) of control and 23/43 (53%) of BCG-treated patients. Muscle invasive and/or metastatic disease occurred with equal frequency in the two groups, but was significantly delayed by BCG treatment (P = .012). Cystectomies were required in 18/43 (42%) control and 11/43 (26%) BCG-treated patients. Median time to cystectomy was 8 months for control v 24 months for BCG-treated patients. Based on initial treatment, survival was improved by BCG therapy (P = .032) (median follow-up 6 years). These results suggest that in high-risk patients intravesical BCG can delay disease progression, prolong the period of bladder preservation, and increase overall survival.