OBJECTIVE. The objective of our study was to assess the technical success, safety, and oncologic and renal function outcomes of CT-guided percutaneous thermal ablation for synchronous multiple renal masses in a single session. MATERIALS AND METHODS. A retrospective analysis of 23 patients (16 men and 7 women; median age, 70 years) with biopsy-proven multifocal renal cell carcinoma (RCC) masses treated with radiofrequency ablation (RFA), cryoablation, or microwave ablation (MWA) was performed. Preablation, postablation, and follow-up serum blood urea nitrogen, creatinine, and estimated glomerular filtration rate (GFR) levels were recorded to evaluate the stability of renal function. Technical success, complications, treatment response, oncologic outcome, and overall survival were assessed. RESULTS. Biopsy-proven RCCs were treated in 23 patients. Median tumor size was 2.3 cm (range, 1.0-4.0 cm). The mean RENAL (radius, exophytic vs endophytic properties, nearness of tumor to the collecting system or sinus, anterior vs posterior, location relative to polar lines) nephrometry score was 6.3 (range, 4.0-10.0); mean PADUA (preoperative aspects and dimensions used for anatomical) score, 7.8 (range, 6.0-11.0); and mean centrality index (Cindex), 3.1 (range, 0.7-6.8). The mean ablation time was 23 minutes (range, 3-24 minutes). Technical success was achieved for 100% of tumors. Of the 49 complications, nine (18%) were classified as Clavien-Dindo grade I complications. Complete response was achieved in 41 of the 49 (84%) tumors. Local progression-free, RCC-specific disease-free, and overall survival rates during the imaging follow-up time (mean, 3.1 years; range, 0.1-9.6 years) were 96% (22/23), 100% (23/23), and 91% (21/23), respectively. CONCLUSION. CT-guided percutaneous thermal ablation is a safe, effective, and durable treatment intervention for multifocal renal masses.