The Food and Drug Administration approval of ruxolitinib for treatment of myelofibrosis and polycythemia vera has changed the management of patients with myeloproliferative neoplasms. Yet the impact of this therapy on risk of thrombosis, a major cause of morbidity and mortality among these patients, remains unknown. The aim of this study was to evaluate the impact of ruxolitinib on the risk of thrombosis among patients with polycythemia vera or myelofibrosis. Following identification of randomized controlled trials comparing ruxolitinib to standard care or placebo, rates of thrombosis, including venous and arterial thrombosis, were analyzed using fixed effects models. Rates of thrombosis were significantly lower among patients treated with ruxolitinib [risk ratio 0.45, 95% confidence interval (CI) 0.23-0.88]. Subgroup analysis of venous and arterial thrombosis demonstrated similar risk ratios, which did not reach statistical significance (risk ratio 0.46, 95% CI 0.14-1.48 and RR 0.42, 95% CI 0.18-1.01, respectively). In conclusion, our analysis suggests that JAK2 inhibition with ruxolitinib decreases the risk of arterial and/or venous thrombosis in patients with polycythemia vera or myelofibrosis. These findings will require confirmation in a prospective study. Copyright (C) 2016 Wolters Kluwer Health, Inc. All rights reserved.