We analysed our population of renal transplant recipients treated with cyclosporin (CsA) and prednisolone with respect to clinically evident de novo malignancies. Eighteen of 598 patients (mean age 35.6 (1 73) years receiving their first renal graft between 1 May 1981 and 31 December 1986 developed a malignancy at a mean interval of 33.5 months. Types of malignancy were squamous carcinoma of the skin (1), carcinoma of the tonsils (1), urothelioma (5), renal-cell carcinoma (2), adenocarcinoma of colon and liver (3), metastic adenocarcinoma of the lung (1), teratocarcinoma of the testis (1), breast cancer (1), Hodgkin's lymphoma in the renal allograft (1), carcinoma of the uterus (1), and carcinoma of the prostate (1). Six cases were observed in the age group 40 49 years (3%), but only three in age group 20 29 years, and nine cases in patients older than 50 years. No malignancy emerged in children (age group <19 years) and in patients with pretransplant malignancies. Five patients with analgesic abuse (n = 21 of 598 patients) developed malignant urotheliomas. It is concluded that de novo malignancies constitute a heterogeneous group with no obvious risk attributable to CsA treatment. As previously reported there is a special risk of malignant urotheliomas in patients with analgesic nephropathy. The risk in children seems to be low. We did not observe the high incidence of lymphomas and skin cancer reported by other groups. © 1990 European Dialysis and Transplant Association-European Renal Association.