In 1981, a black man had adenocarcinoma of the colon. In 1986, he had a sebaceous adenoma and the diagnosis of the Muir-Torre syndrome was established. The patient was found to be HIV sero-positive in 1986, and 8 years later fulfilled the CDC criteria for AIDS. During 1989 to 1993 the CD4 count was > 200 cells/ml and the patient had 2 sebaceous tumors, 1 basal cell carcinoma and 1 keratoacanthoma. In 1994 to 1996, the CD4 count was < 200 cells/ml and the patient developed 18 sebaceous tumors and a poorly differentiated adenocarcinoma of the finger which metastasized to axillary lymph nodes. Microsatellite analysis of tumor DNA from a sebaceous adenoma and adenocarcinoma of the finger revealed widespread microsatellite instability. The interaction of AIDS with the behavior of the tumors in the Muir-Torre syndrome has not previously been reported. Although our patient had an increase in the number of new sebaceous tumors at the same time he experienced deterioration of the immune system, he is doing well 15 years after resection of adenocarcinoma of the colon and 16 months after metastatic poorly differentiated adenocarcinoma of the skin. This follows the previously observed tendency for cancers of the Muir-Torre syndrome, especially those displaying widespread microsatellite instability, to be less lethal than their histologically similar counterparts in people without Muir-Torre syndrome.