We investigated the prognostic importance of plasma myeloperoxidase levels in patients with ST-elevation myocardial infarction (STEMI) at long-term follow-up, and we analyzed the correlations between plasma myeloperoxidase levels and other biochemical values. We evaluated 73 consecutive patients (56 men; mean age, 56 +/- 11 yr) diagnosed with acute STEMI and 46 age- and sex-matched healthy control participants. Patients were divided into 2 groups according to the median myeloperoxidase level (Group 1: plasma myeloperoxidase68 ng/mL). Patients were monitored for the occurrence of major adverse cardiovascular events (MACE), which were defined as cardiac death; reinfarction; new hospital admission for angina; heart failure; and revascularization procedures. The mean follow-up period was 25 +/- 16 months. Plasma myeloperoxidase levels were higher in STEMI patients than in control participants (82 +/- 34 vs 20 +/- 12 ng/mL; P=0.001). Composite MACE occurred in 12 patients with high myeloperoxidase levels (33%) and in 4 patients with low myeloperoxidase levels (11%) (P=0.02). The incidences of nonfatal recurrent myocardial infarction and verified cardiac death were higher in the high-myeloperoxidase group. In multivariate analysis, high plasma myeloperoxidase levels were independent predictors of MACE (odds ratio=3.843; <95% confidence interval, 1.625-6.563; P=0.003). High plasma myeloperoxidase levels identify patients with a worse prognosis after acute STEMI at 2-year follow-up. Evaluation of plasma myeloperoxidase levels might be useful in determining patients at high risk of death and MACE who can benefit from further aggressive treatment and closer follow-up. (Tex Heart Inst J 2012;39(4):500-6)