Overt hyperglycemia has been associated with adverse clinical outcomes in patients with ST-segment elevation myocardial infarction (STEMI). The association of hypoglycemia and mild hyperglycemia with angiographic outcomes and the effect of clopidogrel on these outcomes have not been extensively evaluated. Patients with STEMI enrolled in the CLARITY-TIMI 28 trial (n=3,491) were divided into 6 groups based on admission blood glucose level (<81, 81 to 99, 100 to 125, 126 to 149, 150 to 199, and >199 mg/dl). Angiographic and clinical outcomes were analyzed. Thirty-day mortality was increased (p<0.001) in patients with hypoglycemia (glucose<81 mg/dl, 6.3%) and severe hyperglycemia (glucose>199 mg/dl, 10.4%) compared with the euglycemic group (glucose 81 to 99 mg/dl, 2.6%). Occlusion of the infarct-related artery (IRA; Thrombolysis In Myocardial Infarction flow grade 0/1) at scheduled angiography was more common with increased glucose (9.3% for glucose 81 to 99 mg/dl, 15.6% for glucose>199 mg/dl, p=0.004). Multivariable analysis demonstrated that hyperglycemia was associated with a twofold increase in the composite of an occluded IRA, death, or recurrent MI before angiography (glucose>199 mg/dl, odds ratio 1.93, 95% confidence interval 1.17 to 3.18, p=0.01; glucose 150 to 199 mg/dl, odds ratio 2.04, 95% confidence interval 1.30 to 3.22, p=0.002). There was no significant interaction between clopidogrel administration and the association of glucose and IRA patency (p interaction=NS). In conclusion, in patients with STEMI, hypoglycemia and severe hyperglycemia are associated with increased 30-day mortality. IRA patency after fibrinolytic administration is related to admission glucose independent of clopidogrel administration.