The purpose of this study was to assess the safety, technical results and clinical outcomes of CT-guided percutaneous microwave ablation of stage T1a renal cell carcinoma. This retrospective study investigated consecutive patients who underwent CT-guided microwave ablation for T1a renal cell carcinoma from October 2015 to May 2019. Patient demographics of tumor characteristics, comorbidities, technical details and clinical outcomes were evaluated. Local progression-free survival and overall survival rates were estimated using the Kaplan-Meier method. RESULTS. One hundred six patients (70 men [mean age ± standard deviation, 68.5 years ± 8.9; range, 49-86 years] and 36 women [mean age, 69.5 years ±10.0; range, 50-88 years]; overall mean age, 68.8 years ± 9.2; range, 49-88 years) with 119 T1a renal cell carcinomas were treated with CT-guided microwave ablation. Technical success was achieved for 100% of tumors. Complete response was achieved in 101 (95.3%) patients and partial response was achieved in 5 (4.7%) patients. Local progression-free survival was 100.0%, 92.8%, and 90.6% at 1-, 2-, and 3-years respectively. Overall survival was 99.0%, 97.7%, and 94.6% at 1-, 2-, and 3-years respectively. Six patients (5.7%) had 7 complications (Clavien-Dindo Grade I, SIR category A, = 5; Clavien-Dindo Grade III, SIR category B, = 2) within 30 days of the procedure. CT-guided percutaneous microwave ablation is associated with high rates of technical success, excellent local progression-free survival and overall survival, and low complication rate for stage T1a renal cell carcinoma.