BACKGROUND: The relationship between renal dysfunction and mortality in patients with myocardial infarction (MI) has been extensively investigated, but there are limited data about this relationship in patients presenting with non-ST-segment-elevation MI and unstable angina. Therefore, the aim of the present study was to investigate whether renal insufficiency is an independent predictor for in-hospital mortality among such patients. METHODS AND RESULTS: Two thousand a hundred and seventy-two patients presenting with acute coronary syndrome (ACS) in 6 Greek hospitals were enrolled. Creatinine clearance rates were estimated by the Cockcroft-Gault formula. Five percentage of patients presented with severe renal dysfunction, 27% with moderate dysfunction and the other 68% were normal. Patients with moderate or severe renal dysfunction were older, more likely to be women and more likely to have history of hypertension and diabetes mellitus compared with those with normal renal function. In comparison with patients with normal renal function, those with moderate and severe renal dysfunction were respectively 3- and 12-fold more likely to die. Moreover, moderate and severe renal insufficiency continued to be a prognostic factor for mortality, even after controlling for potential confounders. CONCLUSIONS: Creatinine clearance rate is an important independent predictor of in-hospital mortality, so patients with ACS complicated by renal dysfunction should receive more aggressive medical care.