This is a retrospective analysis of 147 evaluable patients, with histologically proven renal cell carcinoma, who were referred to our center between 1977 through 1988. All patients with disease limited to the kidney underwent nephrectomy. Post-operative megavoltage irradiation, with a median dose of 46 Gy, was given to 56 patients, using parallel opposing portals, or multiple field technique. Five and 10 year actuarial survivals in irradiated patients (Rt+) were 50 and 44%, respectively, and in non-irradiated patients (Rt-) 40 and 32%, respectively. The disease recurred locally in a total of 19 patients; 16 had tumor bed recurrence and three had scar recurrence. Local recurrence by stage was as follows: T2 N0M0: RT+ 0/17, RT- 2/28; T3 N0M0: RT+ 4/37 (10%), RT- 11/30 (37%) (p less than 0.05); T4 N0M0: RT+ 1/2, RT- 1/5. Two of the local recurrences in irradiated patients developed in a surgical scar which was not included in the treatment volume. Significant toxicity developed in three patients (5%). It is concluded that post-operative irradiation can reduce local recurrence rate in T3 N0M0 renal cell carcinoma. It is recommended that the surgical scar should always be included in the treatment volume and irradiated to a full dose.