A patient with pemphigus foliaceus, derived from pemphigus erythematosus, developed Kaposi's sarcoma characterized by wide-spread skin nodules on the extremities after 5-month treatment with large doses of prednisone. The patient died one year later. We conclude that the immunosuppressive treatment with prolonged large doses of prednisone is attributable to the impairment of cellular immunity and the evolution of Kaposi's sarcoma.