The aim of our study was to investigate whether osteoprotegerin (OPG) is related to in-hospital major adverse cardiac events (MACE) and reperfusion parameters in patients with ST elevation myocardial infarction (STEMI). The OPG/receptor activator of nuclear factor-kappa B (RANK)/RANK ligand pathway has recently been associated with atherosclerosis. OPG is a predictor of cardiovascular events in patients with acute coronary syndrome. This study included 96 consecutive patients with STEMI undergoing primary percutaneous coronary intervention (PCI). Two groups with equal number of patients were formed according to median OPG level. The association of OPG levels on admission with post-procedural reperfusion parameters, and in-hospital MACE were investigated. Patients with higher OPG levels displayed higher neutrophil/lymphocyte ratio, admission troponin, admission glucose, and high-sensitive C-reactive protein. Higher OPG levels were associated with increased thrombolysis in myocardial infarction (TIMI) risk score, TIMI risk index, pain to balloon time, need for inotropic support, shock, and MACE, mainly driven by death. Reperfusion parameters were not different between the two groups. TIMI risk score, TIMI risk index, myocardial blush grade, estimated glomerular filtration rate (eGFR), number of obstructed vessels, and OPG significantly predicted adverse cardiac events. Multiple logistic regression analysis revealed OPG as an independent predictor of MACE as well as eGFR, number of obstructed vessels, and corrected TIMI frame count. OPG, a bidirectional molecule displaying both atheroprotective and pro-atherosclerotic properties, is currently known as a marker of inflammation and a predictor of cardiovascular mortality. The present study, for the first time, demonstrated that an increased OPG level is related to in-hospital adverse cardiovascular events after primary PCI in patients with STEMI. (c) 2012 Japanese College of Cardiology. Published by Elsevier Ltd. All rights reserved.