The purpose of this study is to determine the incidence of the malignant tumors in Tunisian renal transplanted population and to establish the risk factors to develop a cancer in transplanted kidneys. Through a retrospective study about 403 renal transplants cases between June, 1986 and May 2005, 31 patients developed a de novo cancer. The average age at the time of transplantation was 36 years and it was 42 years at the time of diagnosis. The average delay of appearance is 74month.42 % of the patients had a positive serology for cytomegalovirus. In conclusion, cancers post-transplantation are frequent and contributing to mortality. The incidence of this pathology can be reduced by taking into account the age of the recipient and the histocompatibility between donor and recipient.