In 661 renal transplantations, 2 potentially migrated tumours (0.38%), 5 preexisting neoplasias (0.76%), and 31 "de novo" tumours were seen in 29 patients (4.4&). Although of very low incidence, the likelihood of tumour migration from elderly donors, given the circumstances surrounding removal, offers a high risk. None of the preexisting neoplasias relapsed following transplant. The highest prevalence was seen in skin (40%), lung (13%), kidney (13%) and bladder (6.6%) "de novo" tumours. Incidence of lymphoma was low. Dominant etiological factors of the recipient were older age, effective and tolerated immunosuppression, viral infections, environmental agents and antigenic stimulation of the graft. Skin lesions have responded well to local treatment, without need to discontinue immunosuppression, a measure that is mandatory in other malignant tumours. Also, the conclusions of a round table during the 25th National Meeting of Urotransplantation of the Spanish Association of Urology held in 1994 on "Oncology and Renal Transplantation" are presented.