The prevalence of metabolic syndrome (MS) was determined in patients aged < or =45 years who presented with acute myocardial infarction and underwent primary percutaneous coronary intervention. Two hundred twenty-three consecutive patients aged 18 to 45 years who underwent cardiac catheterization for acute myocardial infarction from June 2001 to December 2004 were reviewed. MS was diagnosed by National Cholesterol Education Program Adult Treatment Panel III guidelines (modified by substituting body mass index > or =28.8 kg/m2 for waist circumference). One hundred sixty-one patients met all 5 criteria for MS available for evaluation. Seventy-six of these patients (47%) met > or =3 of the 5 criteria for MS. Sixteen patients with MS (21%) and 5 patients without MS (6%) had diabetes mellitus. The prevalence of each criterion was significantly higher (p <0.05) in the MS group. Average Framingham risk scores were 7.0 and 4.5 for patients with and without MS, respectively. The prevalence of smoking, male gender, and family history of premature coronary artery disease were the same for the 2 groups. In conclusion, MS was highly prevalent in this population of young patients with acute myocardial infarction.