Aim. - To determine the incidence and main characteristics of cerebrovascular events as the presenting manifestations of myeloproliferative neoplasm (MPN). Methods. - The Hematology in Lyon (HEMILY) registry is a prospective database (763 patients) of all cases of MPN diagnosed since 2005 in the Rhone-Alpes district of France. The MPN cases were divided into four groups: polycythemia vera (PV); essential thrombocythemia (ET); myelofibrosis (MF); and atypical MPN. The ischemic stroke subtype was classified according to TOAST criteria. Results. - A stroke history revealed MPN in 35 (4.3%) patients: 22 (63%) had an ischemic stroke; eight (23%) had a transient ischemic attack; four (11%) had cerebral venous thrombosis; and one (3%) had hemorrhagic stroke. All patients had hemoglobin and/or platelet count abnormalities. In addition, 12 (34%) patients had PV, 21 (60%) had ET, one (3%) had MF and one (3%) had atypical/unclassified MPN. The JAK2 V617F mutation was found in 83% of patients. In 18 (51%) patients, an additional mechanism of stroke was present (atherosclerosis in 10 patients, atrial fibrillation in one patient and dissection in another). The median NIHSS score at entry was 2, and the median modified Rankin Scale score at 3 months was 0. Compared with the general MPN population, stroke-MPN patients presented with significantly higher levels of hemoglobin (P < 0.001) and were more frequently positive for the JAK2 V617F mutation (P = 0.044). Conclusion. - Stroke revealing MPN is rare. However, careful attention should still be paid to blood counts even in patients with obvious stroke etiologies, as early diagnosis permits prompt treatment and decreases the risk of recurrence, thus limiting morbidity and mortality. (C) 2016 Elsevier Masson SAS. All rights reserved.