Background Outcomes after percutaneous coronary intervention (PCI) for patients with acute myocardial infarction (AMI) complicated by renal insufficiency have been well described However data regarding admission serum creatinine and coronary and myocardial flow are scant The aims of this study are to evaluate the effects of admission serum creatinine on coronary blood flow and prognosis in ST segment elevation myocardial infarction (STEMI) patients undergoing primary PCI Methods A total of 495 patients undergoing primary PCI for STEMI within 12 hours after symptom onset were studied Patients were divided Into two groups according to admission serum creatinine level 1) elevated serum creatinine group (elevated group serum creatinine a >= 1 3 mg/dl) and 2) normal serum creatinine group (normal group serum creatinine < 1 3 mg/dl) Results Elevated serum cream-line was observed in 86 patients Univariate analyses showed statistical differences between normal and elevated serum creatinine groups in age gender number of diseased vessels hypertension previous MI serum creatinine level and Killip's grades on presentation Corrected TIMI frame count (CTFC) in the elevated group was more than in the normal group and TIMI myocardial perfusion grades (TMPG) 0-1 were more frequent (5 6% and 12 8% p < 0 05) Elevated admission serum cream-line was an independent predictor of poor myocardial perfusion (adjusted relative risk [RR] 3 93 95% confidence interval [CI] 1 13-6 84) and a higher rate of 1-year mortality in STEMI patients undergoing primary PCI (adjusted RR 1 41 95% CI 1 24-2 691) Conclusions The elevated admission serum creatinine levels are associated with impaired myocardial flow and poor prognosis in STEMI patients undergoing primary PCI