The development of de novo malignancy in renal transplant recipient is one of the most troublesome problems during long-term follow-up. We reviewed our experience of malignancies in renal transplant recipients in SNUH. Among the 625 cases of renal transplantation performed in SNUH from July 1969 to July 1998, 18 cases of de novo malignancies developed in 17 patients: Kaposi sarcoma (6 cases), mucocutaneous cancer (5), post-transplant lymphoproliferative disease (2), bladder cancer (2), hepatoma (2), and stomach cancer (1). The cumulative incidences of cancer in 1, 5, and 10 years were 1.04%, 1.75%, and 2.63% respectively. Four cancers (3.7%) developed among the 109 patients who received azathioprine -based immunosuppression, and 14 cancers (2.7%) in cyclosporine-based immunosuppression. Malignancy was diagnosed at the age of 44.1 (range 25∼59) years and 69.9 (range 2∼177) months after kidney transplantation. Nine patients received surgical treatment including curative local excision in 5 and graft nephrectomy in one with PTLD in the allograft. Chemotherapy and radiotherapy was done in 7 and 2 patients respectively. Transarterial embolization was done in 1 patient with multiple hepatoma. Reduction or withdrawal of immunosuppression was performed in all patients except five, treated with curative local excision. Total 9 patients died and 3 graft loss occured in 3 survivors due to chronic rejections and allograft nephrectomy. The 5- and 10- year survival rate in the patients with malignancy was 79.3% and 50.5%, which is poorer than those without malignancy (88.6%, 83.0%; P＜0.001). Careful surveillance of malignancy in renal allograft recipients is highly recommended.