Incidence of cutaneous T cell lymphoma and other rare skin cancers in a defined population. Between 1970 and 1984 in Rochester, Minnesota, rare skin cancers developed in 15 local residents: cutaneous T cell lymphoma (six subjects), dermatofibrosarcoma protuberans (four), adenocarcinoma of sweat glands (two), Merkel cell carcinoma (one), liposarcoma (one), and extramammary Paget's disease (one). These cases were identified through a unique computerized retrieval system that is maintained at the Mayo Clinic for the population of Rochester, Minnesota. The annual incidences of these cancers in the Rochester population were 0.9, 0.5, 0.3, 0.2, 0.2, and 0.2 per 100,000 residents, respectively (standardized to 1980 U.S. population). To our knowledge, this is the first report of the incidences of these rare skin cancers in a well-defined population. 