Human papillomavirus (HPV) is associated with carcinoma of the cervix but not with carcinoma of the endometrium. HPV 16 is the type most commonly detected in squamous cell carcinomas from this site, whereas HPV 18 predominates in adenocarcinomas. We analyzed eight anal carcinomas for HPV DNA using the polymerase chain reaction and type-specific (open reading frame E6) primers for HPV 16, 18, 31, and 35. HPV DNA sequences were amplified in two of six anal adenocarcinomas and, in each case, the type was HPV 18. Sequences homologous to HPV 16 were amplified in each of two anal squamous cell carcinomas; one also contained HPV 18. No amplification was detected in any of seven adenocarcinomas of the rectum or colon or in three adenomatous polyps of the colon. It is concluded that HPV is associated with anal adenocarcinomas but not colorectal adenocarcinomas. The reason(s) why HPV is associated with adenocarcinoma of the anus and cervix but not with the rectum and endometrium, despite the close proximity, requires further study.