Background: Polycythemia Vera (PV) is a myeloproliferative neoplasm characterized by unregulated red blood cell production. Most patients (pts) harbor a JAK2 mutation and must have erythrocytosis or elevated red cell mass for diagnosis (DX). Pts are at increased risk of thrombosis. Current treatments include aspirin, therapeutic phlebotomy (TP), and cytoreductive therapy such as hydroxyurea (HU). In 2014, based on the RESPONSE study, ruxolitinib (rux), a selective JAK inhibitor, was approved for second line treatment after intolerance or inadequate response to HU. A recent real-world analysis of rux in PV showed durable hematocrit (HCT) control and decreased need for TP (Coltoff 2020). Despite emerging clinical reports, real-world data on HCT control, dose adjustment, and thrombotic risk with rux are extremely limited. Methods: A retrospective chart review from three centers was performed to evaluate PV pts treated with rux between Dec 2014 and Dec 2019. Pts age <18 at rux start, who received rux through investigational studies, and/or who had myelofibrosis were excluded. Data cutoff was May 30, 2022. Results: 69 patients were identified. Median time from PV DX to rux start was 4.4 yrs (range 0.1 to 40.2), and median follow-up from start of rux was 3.3 yrs (range 0.1 to 6.3). Pt characteristics: 37 (54%) Male, 59 pts (86%) White, 4 (6%) Black, and 64 (93%) Non-Hispanic. The most common reasons for starting rux were HU intolerance (46%), uncontrolled platelet count (28%), and symptom burden (19%). Median time on rux was 2.4 yrs (range 0.1 to 6.3); 43 pts (62%) remained on rux at data cutoff. A total of 6 pts (9%) received less than 3 months of rux before discontinuation, 8 pts (12%) received less than 6 months of rux. 41% pts (27/66), did not have HCT control (HCT <45%) within 1 month prior to rux start. Of evaluable pts, HCT control rates at 3 and 6 months were 88% (52/59) and 89% (47/53) respectively. Phlebotomy frequency in the 3-month periods before and after rux start were known for 48 pts; 21 (44%) experienced a decrease in phlebotomies within 3 months after initiation of rux, 20 (42%) remained stable, and 7 (16%) saw an increase (ranging from +1 to +3). Twelve pts (17%) required dose reductions/suspensions due to cytopenias. One pt experienced an acute pulmonary embolism while on rux (4.4 yrs after rux initiation). The pt was diagnosed with T cell lymphoma while on rux and the thrombotic event was attributed to lymphoma. This pt achieved HCT control on rux at 3 and 6 months. No arterial thromboses were observed. Conclusions: In this real-world analysis, rux was highly effective in controlling HCT in the vast majority of PV pts by 3 and 6 months. PV pts treated with rux rarely developed thrombosis. Rux was well tolerated, and few patients required dose reduction or discontinuation.