The authors report 2 cases of Kaposi's sarcoma in whose immunosuppressive therapy is implicated. In a 47-year-old Italian man, cutaneous lesions were rapidly aggravated after a renal transplant and treatment with corticosteroids and azathioprine; new lesions appeared close to an arteriovenous fistula of the forearm. In a 83-year-old Algerian man, Kaposi's sarcoma appeared during steroid therapy for bullous pemphigoid. The role of acquired immunosuppression, local predisposition and genetical factors are reviewed and discussed for the pathogenesis of Kaposi's sarcoma.