Described is a patient with multiple myeloma who, during long-term treatment with alkylating agents, developed cutaneous Kaposi's sarcoma. Patients with multiple myeloma, unlike those with malignant lymphoma, do not usually develop Kaposi's sarcoma during the natural course of the disease. It is suggested that the immunosuppression resulting from the long-term alkylating agent therapy for multiple myeloma may have prediposed this individual to the development of Kaposi's sarcoma.