One hundred fifty-six consecutive cases of carcinoma of the anal canal and margin diagnosed between 1959 and 1986 were reviewed. There were 27 cases between 1959 and 1967, 41 between 1968 and 1976, and 88 between 1977 and 1986. Although the female-to-male ratio remained constant at 1.5:1, a high-risk group emerged, consisting of male patients with admitted homosexuality, bisexuality, or a history of anal condylomata acuminata. During the earliest period, 8 percent of male patients were in this group; this subset rose to 72 percent during the latest period (P less than .05). While the number of anal margin cancers has decreased, there has been a steady rise in the number of anal canal and in situ carcinomas, especially in the high-risk group.