The incidence of malignancies in recipients of renal transplants was compared to that in non-grafted patients on maintenance dialysis as reported to the EDTA-ERA Registry and in the general population as recorded by the cancer registries of England and Wales, of Sweden, of the (former) German Democratic Republic, and of Lombardy and Varese in Northern Italy. For tumours known to be associated with immunosuppression, namely Kaposi's sarcoma, non-Hodgkin lymphoma and the common malignancies of the skin (except melanoma), an increased incidence was confirmed for the transplanted population Thyroid carcinoma and hepatoma were found to be more frequent in non-grafted patients on dialysis as well as after renal transplantation. An increased incidence of cancer of the cervix and of the body of the uterus was recorded only for young cohorts with a functioning graft but not for women after menopause. Most of the other malignancies had similar incidences in grafted and non-grafted populations which did not differ from those in the general populations of the cancer registries except cancer of the colon which was slightly more frequent, particularly at 10-20 years after the first transplant operation. Survival after diagnosis of cancer at the most frequent sites, such as bronchopulmonary, breast, oesophagogastric and colorectal cancer, did not differ between non-grafted patient groups on dialysis and those who developed the tumour while carrying a functioning renal transplant. Although certain specific malignancies such as non-Hodgkin lymphoma and skin tumours occur more frequently in recipients of renal grafts, the risk of developing cancer has been exaggerated and survival after diagnosis of the common cancers does not appear to be affected to any great extent by immunosuppressive therapy.