Organ transplant recipients treated with immunosuppressive therapy are prone to develop malignancies particularly squamous cell carcinomas of the skin, non-Hodgkin's lymphomas, Kaposi's sarcomas, carcinomas of the vulva and perineum, in situ carcinomas of the uterine cervix, renal carcinomas, hepatomas, and various sarcomas. The earliest tumors to appear are the Kaposi's sarcoma at an average of 21 months after transplantation, and the latest are carcinomas of the vulva and perineum, at an average of 112 months after transplantation. The tumors that develop in cardiac allograft recipients compared with renal transplant recipients are predominantly non-Hodgkin's lymphomas and more rarely, skin, uterine cervical and vulvar tumors. Major factors accounting for these differences are the intensity of immunosuppressive therapy given to the cardiac patients and the much longer follow-up of the renal allograft recipients.