Unit. Patients were aged 24-85 years (median 68), and were diagnosed as having essential thrombocythemia (ET) (n = 149, 45%), polycythaemia vera (PV)(n = 94, 29%), primary myelofibrosis (PMF)(n = 69, 21%) and unclassifiable MPN (n = 17, 5%). Diagnosis were made according to the 2008 WHO Classification. JAK-2 mutation status was either established or revised in our center, but was unknown in 55 (17%) patients. Data about treatment and cardiovascular and thromboembolic incidents was retrieved from medical records. Results: Forty patients (12%) developed thrombosis after median of 36 (range 1-240) months from the time of diagnosis. Fifteen (5%) patients developed venous thrombosis, twenty-four (7%) arterial, while one (0,3%) patient both type of thrombosis. Regarding the disease type, thrombosis was described in 16 patients with ET (11%), 18 with PV (19%) and 6 with PMF (8%). The risk of thrombosis was the highest in patients with previous thrombotic events, but did not correlate with the type of therapy (cytoreductive and/or antiagreggation) nor the JAK-2 status. Summary/Conclusion: The risk of both arterial and venous thrombosis was found to be increased in patients with MPN even after introducing appropriate treatment. The highest risk of post treatment thrombosis was found in patients with previously diagnosed thrombotic events.