The impact of the metabolic syndrome/insulin resistance syndrome (MS/IRS) on the severity and prognosis of acute ST elevation myocardial infarction (STEMI) treated with primary percutaneous coronary intervention (PCI) was assessed using the American Association of Clinical Endocrinologists and American College of Endocrinology (AACE/ACE) definition from 2003. A total of 385 patients having suffered acute STEMI and treated with primary PCI over a two-year period were divided into two groups (with and without MS/IRS) and compared according to the parameters of severity (clinical, laboratory, echocardiography, coronary angiography parameters and complications) and prognosis using major adverse cardiovascular events (MACE) during the six-month follow-up of acute STEMI. In comparison with control group, the MS/IRS group of patients had worse or similar results of almost all study parameters of severity (hospital days 6.5 versus 6.5, cardiogenic shock 2.9% versus 2.6%, cardiac arrest 6.8% versus 5.2%, reinfarction 0.5 versus 1.6%) and prognosis (total MACE 30.7 versus 30.7%), however, none of the differences reached statistical significance. It is concluded that the unexpected lack of such differences in MS/IRS could be due to the absence ofwaist-to-hip ratio in the definition and other open questions in metabolic syndrome in general.