Collateral circulation plays a key role in stroke and cardiovascular diseases. Hyperglycemia is known to aggravate cerebral ischemia. However, whether hyperglycemia directly contributes to collateral circulation after acute ischemic stroke is unknown. We sought to investigate the relationship between collaterals and fasting glucose levels in acute ischemic stroke patients. 45 patients (mean age, 61.9 +/- 11.4 years; 29 males) underwent acute ischemic stroke were enrolled from September 2014 to August 2015. M1 segment of middle cerebral artery (MCA) +/- intracranial internal carotid artery (ICA) occlusions were measured using Digital Subtraction Angiography (DSA). Two neurologic clinical specialists evaluated the DSA images and graded the cerebral collaterals using Collateral Flow Grading System (Grade 0-4). Poor collaterals (Grade 0-2) were observed in 32/45 (71.1%) patients. Univariate analysis identified that patients with poor collaterals at baseline had higher fasting glucose levels at admission (P=0.025). At multivariate analysis, fasting glucose at admission did not achieve independent predictor status for poor cerebral collaterals (P=0.120). This study of 45 patients shows that hyperglycemia indicate higher risk of poor cerebral collaterals in patients underwent acute ischemic stroke, but hyperglycemia is not an independent predictor of poor cerebral collaterals in these patients.