Hyperglycemia has been shown to be a powerful predictor of worse outcome after ST-segment-elevation myocardial infarction (STEMI), which could be related to impaired myocardial reperfusion. This study investigated the association between hyperglycemia and ST-segment resolution (STR) after thrombolysis. From the French regional Observatoire des Infarctus de Côte-d'Or survey, admission glucose in 371 patients with STEMIs who were treated by lysis<12 hours was analyzed. The single worst lead electrocardiogram before and 90 minutes after lysis was analyzed, and patients were divided into 3 groups according to the degree of STR: none (<30%), partial (30% to 70%), or complete (>or=70%). Of the 371 patients, 101 (27.2%) had no STR, 124 (33.4%) had partial STR, and 146 (39.4%) had complete STR. STR decreased with increasing glycemia (p=0.029), and patients with hyperglycemia (glycemia>or=11 mmol/L) were more likely to have no STR. Moreover, hyperglycemia was an independent predictor of incomplete STR even after adjustment for potential confounders (odds ratio 2.348, 95% confidence interval 1.212 to 4.547). In conclusion, the present study suggests a strong association between hyperglycemia and electrocardiographic signs of reperfusion in patients with STEMIs after lysis and suggests the usefulness of evaluating early glycemic control in the setting of reperfusion for acute myocardial infarction.