Kaposi's sarcoma of the rectum in patients with the acquired immunodeficiency syndrome. We retrospectively reviewed eight patients with biopsy-proven anorectal Kaposi's sarcoma (KS) treated between 1984 and 1989 at San Francisco General Hospital. All patients were homosexual men with the acquired immunodeficiency syndrome (AIDS). The average age was 34 years. Three patients had primary rectal KS without metastases. Five patients had disseminated KS with lesions throughout the alimentary tract, viscera, skin, or local lymph nodes. Three patients were treated with radiation or chemotherapy. Five patients had disseminated KS with lesions throughout the alimentary tract, viscera, skin, or local lymph nodes. Three patients were treated with radiation or chemotherapy. Five patients with advanced AIDS received no specific treatment for anorectal KS. Follow-up ranged from 1 month to 5 years. Three of the untreated patients and the three patients treated with chemotherapy or radiotherapy were alive 1 month to 5 years after diagnosis. Aggressive surgical treatment of anorectal KS is not indicated. 