Anal warts (condylomata acuminata) from seven homosexual men revealed intraepithelial carcinoma (carcinoma in situ) within the condylomatous tissue or in adjacent anal mucosa. All lesions displayed morphologic evidence of papillomavirus infection and two of the seven revealed histologic changes characteristic of herpes simplex infection. This association of viral infection with malignant transformation indicates that persistent or recurrent anal warts should be excised and thoroughly examined by histologic techniques. Since four of the seven patients had histories suspicious for or diagnostic of the acquired immunodeficiency syndrome (AIDS), we further suggest that homosexual men with persistent or recurrent perianal lesions be evaluated for the presence of the syndrome.