One hundred and ten patients with primary epidermoid cancers of the anal canal were treated in a series of prospectively designed, nonrandomized protocols of split-course radiation therapy with concurrent administration of 5-fluorouracil (5-FU) with or without mitomycin. The addition of mitomycin was associated with improved primary tumor control rates (87 vs. 58% at 4 years, p = 0.005) and improved 4-year actuarial cause-specific survival (80 vs. 64%, p = 0.02). Hematologic toxicity was the most frequent acute side effect of mitomycin use. No long-term toxicity was attributed to mitomycin only. Mitomycin appeared to benefit patients principally through improved control of cancer in the irradiated volume; there was no evidence of reduced risk of extrapelvic metastases. Several investigators have reported high rates of control of epidermoid anal cancers with preservation of anorectal function following concurrent treatment with mitomycin, 5-FU, and radiation. Mitomycin’s role in anal cancer is being evaluated in a randomized clinical trial by the Radiation Therapy Oncology Group. The mechanisms of any interactions between mitomycin and radiation or other cytotoxic drugs in clinical practice remain to be determined.