Background: Immunotherapy improves survival in patients with advanced renal cell carcinoma (RCC), but has no established role for perioperative use in patients with localized RCC. Neoadjuvant immunotherapy is a promising strategy in several cancers, and may leverage the primary tumor as antigen source. Methods: We conducted a single institution pilot study of neoadjuvant nivolumab in patients with RCC undergoing nephrectomy with curative intent. Patients were eligible if their risk of metastatic recurrence within the first 12 years was >20% by an established nomogram. After confirmatory biopsy and renal MRI, patients were treated with standard dose nivolumab every 2 weeks for 4 treatments, with a follow-up renal MRI prior to nephrectomy. The primary end points of the study were safety and feasibility defined as being able to complete 3/4 treatments without surgical delay. We evaluated adverse events by CTCAE, surgical safety by Clavien-Dindo classification, and tumor radiographic response by RECIST 1.1. Results: Eighteen (11 men, 7 women; median age 60) were enrolled. All patients had clear cell RCC, median tumor size at baseline was 8.8cm (range 6.4-14.2cm). Median predicted 12-year probability of recurrence was 45% (range 25-71%). All received at least 1 dose of nivolumab; 16/18 patients completed all 4 doses. 17/18 (94%) patients completed at least 3 doses. No patient had notable delay in the timing of their nephrectomy. 4 patients had surgical complications per Clavien-Dindo classification, including 2 with grade 3a chylous ascites after lymphadenectomy. Two patients had nivolumab discontinued for immune-related adverse events, including grade 3 transaminitis and grade 2 arthralgias; a third patient developed grade 4 colitis 4 months after completing nivolumab. All patients had stable disease as the best response prior to surgery. Recurrence-free survival at 2 years was 0.74 (95%CI 0.45-0.90). We analyzed an additional 21 patients with metastatic RCC (20 ccRCC, 1 epithelioid AML) who subsequently had nephrectomy after standard immunotherapy. 15 patients had received ipilimumab+nivolumab, 6 received single-agent PD-1 or PD-L1 inhibitors. 3 (14%) patients achieved a near or complete pathologic response, including a patient with epithelioid AML. Analysis of radiologic and pathologic biomarkers of response are ongoing and will be presented at conference. Conclusions: In this pilot study, there were no new safety signals or delays in surgery with preoperative nivolumab. Neoadjuvant immunotherapy shows preliminary evidence of safety, feasibility and efficacy; biomarker studies may help identify individuals who may have a higher likelihood of response. Clinical trial information: NCT02595918.