From 1968 to 1982, 195 patients with invasive cancer of the anal canal were treated (average age, 67 +/- 11 years; range, 38 to 85 years; sex ratio [women/men]: 5/1). Histology revealed: cloacogenic cancer, 20 cases; squamous cancer, poorly differentiated, 30; moderately differentiated, 68; well differentiated, 77. The initial size of the cloacogenic cancers was smaller than the squamous cancers. Invasion less than half the circumference of the canal was 90 and 74 percent, respectively. No patients with cloacogenic cancer presented with positive inguinal nodes; however, there were 22 unilateral and five bilateral positive nodes in the squamous cancers. All 195 patients received radiotherapy as the first treatment. There were no differences among the patients operated on with respect to sterilized operative specimens, postradiotherapy sequelae, perineal recurrences, and/or visceral metastases in the cloacogenic and squamous cancers. Five-year survival was better in cloacogenic (62 percent) than in squamous cancers (56 percent); this difference was not significant, and was related to the initial size of the tumor. The number of patients with no evidence of disease and good anal function was significantly related to the initial size of the tumor, and was independent of the histologic findings.