This study is a retrospective analysis of malignant tumors in renal transplant recipients. A review of the pertinent literature allowed us to develop a protocol for early diagnosis and treatment of tumors arising in this group of patients.171 renal transplants have been performed over a period of 4 years. The renal grafts had been harvested from cadavers (mean age 32.01 years). All recipients (mean age 44.3 years) were immunosuppressed with prednisone, azathioprine and cyclosporine A.Five "de novo" malignant tumors were detected in 4 patients (2.3%). The tumors were basal cell epithelioma of scalp and gastric adenocarcinoma in the same patient, lymphoma of the CNS, carcinoma of the breast and adenocarcinoma of the colon. The patient with a gastric adenocarcinoma died after a disease-free interval of 28 months, following treatment of the cutaneous lesion. The patient with lymphoma of the CNS had died before receiving treatment and the remaining 2 patients are disease-free at 12 and 6 months' follow-up.The possible role of viruses is underscored. Transplant recipients should be followed very closely since they are likely to develop a tumor, especially of skin and lips. The importance of gynecological and neurological assessment and control of native kidneys cannot be overemphasized. Performing an autopsy on donors can reduce the risk of transplanting tumors. Kidney transplantation should be delayed if the graft recipient has a tumor. Correct diagnosis and treatment will enhance the results in these patients.