Excess of cancer in patients receiving renal transplantation is well-known in Western countries, but information in Japan remains limited. Our study examined whether excess risk is found in patients receiving renal transplantation in Japan. Between 1970 and 1995, 1155 males and 589 females underwent renal transplantation in 6 hospitals, and a total of 12,982 person-years of observation was accumulated. Malignancies developed in 2.6% of patients; O/E ratio was 2.78. Median interval from renal transplantation to tumor development was 58 months. The interval in the patients receiving medication with cyclosporine-A (CyA) (median, 42.5 months) was significantly shorter than that with non-CyA (median, 95.5 months). Median age at the diagnosis of malignancy was 40 years, which is much younger than that in the general population. Relative risk was highest in renal cancer, followed by thyroid cancer, malignant lymphoma and uterine cancer. A distribution of malignancies was different from that reported from Western countries. These findings showed the excess risk of malignancies in Japan with renal transplants, especially in male patients, similar to that observed in Western countries, though the types of malignancy were different.