OBJECTIVE The aim of this study is to report our experience on myocardial infarction (MI) in patients with essential thrombocythemia (ET) and polycythemia vera (PV). METHODS Patients with PV and ET consecutively diagnosed and followed in authors' Department between 1 July 1986 and 30 June 1996. METHODS Over the past 10 years we have followed 170 patients with ET and 149 with PV, diagnosed according to the Polycythemia Vera Study Group (PVSG) criteria. The patients were divided into 3 groups on the basis of the age at diagnosis (group A < 40, B 41-65, C > 65 years). METHODS In all patients with PV phlebotomies and/or myelosuppressive therapy were used to keep haematocrit level lower than 45%. Hydroxyurea was given to patients with ET with a positive history for major vascular complications or with an extreme thrombocytosis. Aspirin therapy (ASA) (100 mg per day) was administered in patients with microvascular disturbances or previous thrombosis (in patients with PV also in the presence of atherosclerotic risk factors). METHODS Frequency of MI in patients with ET and PV with and without ASA therapy. RESULTS 9.4% of patients with ET and 11.4% of those with PV had MI. 17.6% of patients with PV were younger than 40 years at the moment of MI in contrast to 0% of those with ET. 75% of patients with ET and 70.6% of those with PV with MI had atherosclerotic risk factors such as smoking, hypertension, diabetes, dyslipidaemia. All patients with MI received ASA 100 mg daily after thrombosis and four of the ET group developed a transient ischaemic attack (TIA) afterwards. Four subjects with PV during the follow-up had TIAs and two peripheral arteriopathy in spite of ASA treatment. CONCLUSIONS MI is less common in patients with ET younger than 40 years than in older patients. Association of MI and cardiovascular risk factors is frequent in patients with ET and PV. A low dose of ASA could be able to reduce the number of coronary thrombosis without increasing bleeding complications in patients with elevated platelet count and common atherosclerotic risk factors. However, a larger population must be evaluated to confirm our hypothesis.