Thromboses are prevalent in POEMS syndrome, but few risk factors for POEMSassociated thrombosis have been identified. The objective of this study is to identify novel risk factors for POEMS-associated thrombosis. In this retrospective cohort of 230 POEMS patients, 27% developed thrombosis. Arterial events were slightly more common than venous. Stroke accounted for 26% of all thromboses and 53% of arterial events. There were differences in baseline features between the thrombosis group and the no thrombosis group, and these were driven by patients with arterial thrombosis. Risk factors for arterial thrombosis included thrombocytosis, elevated hemoglobin/hematocrit, extravascular volume overload, and splenomegaly. Hyperprolactinemia appeared to be a risk factor for venous thrombosis. The risk of thrombosis was most striking among men with elevated hemoglobin (32% vs. 5%, p < .001) and hematocrit (42% vs. 5%, p < .001) compared to men without. Most thromboses occurred prior to POEMS directed therapy, and most that occurred during therapy happened within 3 months of diagnosis. Twenty-one percent of patients with thrombosis had recurrence. In recognition of high overall rates of thrombosis in this population, all patients with POEMS syndrome should receive prophylactic antiplatelet therapy, and clinicians should consider anticoagulation in patients with risk factors for POEMS-associated thrombosis. 1 | INTRODUCTION POEMS syndrome is a rare, multisystem paraneoplastic disorder driven by an aberrant plasma cell clone. The POEMS acronym, coined by Bardwick in 1980, summarizes five common associated signs and symptoms of this disease (polyneuropathy, organomegaly, endocrinopathy, monoclonal protein, and skin changes). 1 Additional features include papilledema, extravascular volume overload, sclerotic bone lesions, thrombocytosis, elevations in vascular endothelial growth factor (VEGF), and Castleman disease.Although not included in formal diagnostic criteria, the association between POEMS syndrome and thrombosis is well established in case reports and larger observational studies. [2][3][4][5][6][7][8] Thrombosis occurs in 20% to 30% of POEMS patients, and ischemic stroke in 8% to 10%. [5][6][7][8][9] Studies on risk factors for thrombosis in POEMS syndrome, however, are limited and feature conflicting results. In one report, bone