PURPOSE: We assess the feasibility, safety and efficacy of radio frequency ablation of small peripheral renal cell carcinomas. MATERIALS AND METHODS: Five patients with a histologically proven renal cell carcinoma 30 to 40 mm. in diameter were treated with radio frequency ablation. A triple needle electrode was percutaneously advanced into each tumor under sonographic (4 cases) or computerized tomography (CT) (1) guidance. The radio frequency generator was activated for 15 minutes in each location where the electrode had been placed. Patients were then followed with CT and blood tests every 2 months for 6 months and every 3 months thereafter. RESULTS: Four tumors required 1 radio frequency delivery and 1 required 2 applications during the same session. No complications were encountered except for a subcapsular hematoma in 1 patient, which resolved spontaneously. Two patients experienced transient hematuria. Of the patients 4 were discharged from the hospital after 2 days and 1 after 1 day. After 6 to 18 months (median 9) all patients were tumor-free on CT without suppress additional treatment. CONCLUSIONS: In this small preliminary study radio frequency ablation of small peripheral renal cell carcinomas appears to be a feasible, safe and promising technique.