Anal cancer is a type of cancer which arises from the anus, the distal orifice of the gastrointestinal tract. It is a distinct entity from the more common colorectal cancer. The etiology, risk factors, clinical progression, staging, and treatment are all different.

Anal cancer is similar to cervical cancer in many respects - both are typically carcinomas, composed of squamous cells, that arise near a squamocolumnar junction and are strongly associated with infection by certain strains of the human papillomavirus. Anal sex is a significant risk factor for anal cancer. Immunosuppression, which is often associated with HIV infection, also raises the risk of anal cancer. Anal pap smears similar to those used in cervical cancer screening have been studied experimentally for early detection of anal cancer in high-risk individuals.