Superficial transitional cell carcinomas (TCC) of the urinary bladder, defined as those that are restricted to the mucosa or the lamina propria, represent a common condition with a wide spectrum of biologic significance. High-grade superficial TCC, particularly in the presence of lamina propria invasion, has a significant risk of occult or subsequent progression to muscle-invasive or metastatic disease. Such high-risk lesions merit aggressive therapy with repeat resection followed by intravesical therapy, usually in the form of bacille Calmette-Guérin. Criteria for failure of intravesical therapy are not well defined, but persistent cytologic or cystoscopic abnormalities at 6 months are worrisome. Salvage intravesical therapy may sometimes be successful, but early cystectomy should be strongly considered, especially in younger patients. Close surveillance of patients with high-risk superficial TCC is essential.