BACKGROUND Acute kidney injury (AKI) and acute hyperglycemia are associated with unfavorable outcomes. The impact of acute hyperglycemia on the development of AKI after acute myocardial infarction (AMI), however, remains unclear. This study was undertaken to assess the relationship between admission glucose and incidence of AKI after AMI. METHODS AND RESULTS This study consisted of 760 patients with AMI admitted to the National Cerebral and Cardiovascular Center within 48h after symptom onset. Blood sample was obtained on admission and repeated sampling was done at least every 1 or 2 days during the first week. AKI was diagnosed as increase in serum creatinine ≥0.3mg/dl or ≥50% within any 48h. Ninety-six patients (13%) had AKI during hospitalization for AMI, and these patients had higher in-hospital mortality than those without AKI (25% vs. 3%, P<0.001). Patients with AKI had higher plasma glucose (PG) on admission than those without (222±105mg/dl vs. 166±69mg/dl, P<0.001). The incidence of AKI increased as admission PG rose: 7% with PG <120mg/dl; 9% with PG 120-160mg/dl; 11% with PG 160-200mg/dl; and 28% with PG >200mg/dl (P<0.01). On multivariate analysis admission PG was an independent predictor of AKI (odds ratio, 1.10; 95% confidence interval: 1.03-1.18, P=0.02). CONCLUSIONS Admission hyperglycemia might have contributed to the development of AKI in patients with AMI.