Background: Initial safety results from the phase 3b/4 CheckMate 374 study showed that flat-dose nivolumab (NIVO) at 240 mg every 2 wk (Q2W) had a consistent safety profile across patients (pts) with clear cell and non-clear cell advanced RCC. We report updated safety and first disclosure of efficacy for pts with non-clear cell RCC (nccRCC) in CheckMate 374. Methods: Eligible pts in this cohort were adults with advanced or metastatic nccRCC who received 0–3 prior systemic therapies. Pts received NIVO 240 mg IV Q2W for ≤24 mo or until confirmed progression, unacceptable toxicity, or withdrawal of consent. Pts who benefited after 24 mo continued treatment according to the standard of care. The primary endpoint was incidence of high-grade immune-mediated adverse events (IMAEs). Exploratory endpoints included overall survival (OS), progression-free survival (PFS), objective response rate (ORR), and duration of response (DOR). Results: In CheckMate 374, 44 pts had nccRCC. Histological subtypes included papillary (n = 24), chromophobe (n = 7), unclassified (n = 8), and other (n = 5). Most pts with nccRCC (66%) were treatment-naïve. After a median follow-up of 11.1 mo, median OS was 16.3 mo (95% confidence interval [CI] 9.2–not estimable [NE]). OS was similar regardless of baseline PD-L1 expression. ORR was 13.6% (95% CI 5.2–27.4). One pt had complete response (chromophobe histology) and 5 pts had partial response (2 pts with papillary and 1 pt each with chromophobe, collecting duct, and unclassified histology). Median DOR was 10.2 mo (95% CI 5.6–NE). Median PFS was 2.2 mo (95% CI 1.8–5.4). The 1-year PFS rate was 14% (95% CI 5–27). No new safety concerns were identified. No treatment-related grade 5 AEs or grade 3–4 IMAEs were reported. Conclusions: Clinically meaningful antitumor activity was observed in the first prospective study of NIVO monotherapy in nccRCC. Responses were observed in several histological subtypes. The safety profile of flat-dose NIVO at 240 IV Q2W is consistent with the initial outcomes reported from this study and across the NIVO program. Clinical trial information: NCT02596035