Toxicity and disease recurrence are common in patients with non-muscle-invasive bladder cancer (NMIBC) treated with intravesical BCG. Results from a prospective randomized trial in 407 patients with NIMBC show that sequential treatment with mitomycin C and BCG increased the disease-free interval compared with BCG alone (HR = 0.57) and reduced the relapse rate by 13.3%. However, higher toxicity might restrict its use to patients with a high probability of recurrence.