Background: Dual checkpoint inhibition with Anti-PD-1 and anti-CTLA4 checkpoint inhibitors have proven to be effective in several malignancies but their potential role in various rare solid cancers is yet to be established. The efficacy of immunotherapy in vulvar cancer patients has not been explored. This study presents the first results of ipilimumab and nivolumab in vulvar cancers (cohort 35) of the SWOG S1609 Dual Anti-CTLA-4 & Anti-PD-1 blockade in Rare Tumors (DART) trial. Methods: DART is a prospective, open-label, multicenter/multi-cohort phase 2 clinical trial of ipilimumab (1mg/kg intravenously every 6 weeks) plus nivolumab (240mg intravenously every 2 weeks). The primary endpoint was objective response rate (ORR) (RECIST v1.1) (confirmed complete (CR) and partial responses (PR)); progression-free survival (PFS), overall survival (OS), stable disease (SD) > 6 months, and toxicity are secondary endpoints. Results: Sixteen evaluable patients (median age, 55.5 years) were analyzed. 14 cases were of squamous cell carcinoma histology and 2 were of poorly differentiated carcinoma. ORR was 18.8% (3/16, 25% when including one unconfirmed PR). There was 1 CR (SCC; PFS of 465 days) and 2 PR (both SCC; one with 57% regression with PFS of 1022 days, another with 53% regression with PFS of 501 days). Of note, there was one SCC patient with unconfirmed PR that showed 69% regression with PFS of 209 days. Overall clinical benefit rate (CBR; no progression > 6months) was 31.3% (5/16). The median PFS was 2.2 months, 6-month PFS 33%, 1-year PFS 20%. The median OS was 7.6 months, 6-month OS 62%, 1-year OS 44%. The most common adverse events were diarrhea, fatigue, pruritus, anorexia, and nausea (25%, n = 4 each). Grade 3-4 adverse events occurred in 25% of patients (n = 4). There was 1 grade 3-4 adverse event (6.7%) that led to discontinuation, and 1 (6.7%) grade 5 death adverse event. Conclusions: Ipilimumab plus nivolumab in vulvar cancers resulted in an ORR of 18.8% and CBR of 31.3%, with durable responses seen. Correlative studies to determine response and resistance markers are ongoing. Expanded prospective studies exploring the role of immunotherapy in vulvar cancers are warranted. Clinical trial information: NCT02834013.