430 Background: Active surveillance is an alternative to primary intervention aimed at reducing the overtreatment of small renal masses, defined as solid renal masses ≤4.0 cm (clinical stage T1a). Methods: Since 2009, the Delayed Intervention and Surveillance for Small Renal Masses (DISSRM) registry prospectively enrolled 615 patients with small renal masses who chose to undergo primary intervention or active surveillance. Intervention was recommended to patients for masses with an elevated growth rate (>0.5 cm/year) or increased tumor diameter (>4.0 cm). Primary outcomes were cancer-specific survival and overall survival; secondary outcomes included progression-free survival. Progression was strictly defined as growth rate >0.5 cm/year, greatest tumor diameter >4.0 cm, metastatic disease, or elective crossover. Outcomes were evaluated using Kaplan-Meier survival analysis and comparisons were performed using the log-rank test. Results: Of the 615 enrolled patients, 298 (48.5%) chose primary intervention and 317 (51.5%) chose active surveillance. From the active surveillance cohort, 45 (14.2%) patients underwent delayed intervention. Median follow-up time for the entire registry was 2.9 years, with 203 (33.0%) patients followed for 5 years or more. At baseline, patients who chose active surveillance were older (p < 0.001) and had higher comorbidity status (p < 0.001) than those who chose primary intervention. There was no difference in cancer-specific survival at 7 years between primary intervention and active surveillance (99.0% vs. 100%, respectively, p = 0.3). However, overall survival was higher in patients with primary intervention when compared to active surveillance at 5 years (93.0% vs. 80.2%, respectively) and 7 years (91.7% vs. 65.9%, respectively, p = 0.002). The 5-year and 7-year progression-free survival rate in the active surveillance cohort was 76.7% and 48.4%, respectively. Conclusions: In the intermediate-term, active surveillance appears to be as safe as primary intervention for carefully selected patients with small renal masses. As the registry matures, further studies will elucidate the effectiveness of active surveillance in the long-term. Clinical trial information: NCT02346435.