Presentation of the "de novo" tumours developed in two series of renal transplant receptors over the last 16 years. The first series, Historic, comprises the group of 178 patients who were given Azathioprin or Cyclophosphamide plus Prednisone for immunosuppression. The second series, Current, includes 129 patients who received immunosuppressive therapy with Cyclosporin A. Overall incidence of these "de novo" malignant tumours was 4% (13/307), 9 of which corresponded to the Historic Series (incidence, 5%) and 4 to the Current Series (incidence, 3%). Mean time interval from transplantation to diagnosis was 87.3 months (range, 9-177) in the Historic Series and 34.5 (range, 8-67) in the Current Series, the difference being statistically significant (p = 0.02). By locations, skin and lip tumours represent 38.5%, followed in frequency by lymphoma (23%) and lung carcinoma (15%). No urological tumours were recorded.