Purpose: : To compare outcomes of robot-assisted partial nephrectomy (RAPN) and percutaneous tumor ablation (PTA) for completely endophytic renal masses. Methods: : Data of patients who underwent RAPN or PTA for treatment of completely endophytic (three points for “E” domain of R.E.N.A.L. score) were collected from seven high-volume U.S. and European centers. PTA included cryoablation, radiofrequency, or microwave ablation. Baseline characteristics, clinical, surgical, and postoperative outcomes were compared. Recurrence-free survival (RFS) was calculated with Kaplan–Meier analysis. Trifecta was used as arbitrary combined outcome parameter as proxy for treatment “quality.” Multivariable logistic regression model assessed predictors of trifecta failure. Results: : One hundred fifty-two patients (RAPN, n = 60; PTA, n = 92) were included in the analysis. RAPN group was younger ( p < 0.001), had lower American Society of Anesthesiologists score ( p = 0.002), and higher baseline estimated glomerular filtration rate ( p < 0.001). There was no difference in clinical tumor size, clinical T stage, and tumor complexity scores. PTA had significantly lower rate of overall ( p < 0.001) and minor ( p < 0.001) complications. ΔeGFR at 1 year was statistically higher for RAPN (−15.5 mL/min vs −3.1 mL/min; p = 0.005), no difference in ΔeGFR at last follow-up ( p = 0.22) was observed. No difference in recurrences (RAPN, n = 2; PTA, n = 6) and RFS was found ( p = 0.154). Trifecta achievement was higher for RAPN but not statistically different (65.3% vs 58.8%; p = 0.477). R.E.N.A.L. Nephrometry Score resulted predictive of trifecta failure (odds ratio = 1.47; confidence interval = 1.13–1.90; p = 0.004). Conclusions: PTA confirms to be an effective treatment for completely endophytic renal masses, offering low complications and good mid-term functional and oncologic outcomes. These outcomes compare favorably with those of RAPN, which seem to be the preferred option for younger and less comorbid patients.