Objective: The 'no-reflow' phenomenon after a primary percutaneous coronary intervention (pPCI) in patients with acute ST-segment elevation myocardial infarction (STEMI) is a strong predictor of both short- and long-term mortality. We therefore developed and prospectively validated a risk score system in order to identify STEMI patients at high risk in terms of no-reflow after primary PCI. Methods: The first part of our study used data from 1,615 STEMI patients who underwent primary PCI within 12 h from symptom onset. Using logistic regression, we derived a risk score to predict angiographic no-reflow using baseline clinical variables. From this score, we developed a simplified fast-track screen that can be used before reperfusion. In the second part of our study, we prospectively validated the score system using receiver-operating characteristic (ROC) curves with data from 692 STEMI patients. Results: The model included six clinical items: age, neutrophil count, admission plasma glucose, beta-blocker treatment, time-to-hospital admission and Killip classes. The risk score system demonstrated a good risk prediction with a c-statistic of 0.757 (95% CI 0.732-0.781) based on ROC analysis. Conclusion: A simple risk score system based on clinical variables is useful to predict the risk of developing no-reflow after pPCI in patients with STEMI. Copyright (C) 2013 S. Karger AG, Basel