: Philadelphia chromosome negative myeloproliferative neoplasms (MPNs) are associated with increased thrombosis and bleeding risk. Mean platelet volume (MPV) is associated with thrombosis in nonmalignant settings. This study evaluates the association between MPV and thrombosis and bleeding in MPN. Patients with MPN without prior thrombosis, nonhematologic malignancy or anticoagulant use were included in this retrospective analysis. The primary endpoint was arterial or venous thrombosis. The secondary endpoints were any bleeding and major bleeding. MPV was measured at diagnosis and during the index episode. A total of 135 MPN patients met the inclusion criteria. Over a median follow-up of 6.6 years, 23 patients (15.6%) experienced thrombosis. There was no difference in MPV at diagnosis (8.47 vs. 8.73 fl, P = 0.4) or during the index event between patients with or without thrombosis. Twelve patients (8.9%) had a bleeding event, whereas seven (5.2%) had major bleeding. MPV was significantly higher among patients with major bleeding, both at diagnosis (10.04 vs. 8.61, P = 0.005) and during the bleeding episode. There was no association after regression analysis of variables associated with MPV at diagnosis. MPV is not associated with thrombotic events in MPN. The study generates the hypothesis that MPV may be an indirect marker of bleeding in MPN.