Background: Diabetes mellitus (DM) is associated with a wide range of microvascular abnormalities in the brain. These include the dysfunction of the blood brain barrier (BBB). In this study, we test the hypotheses that disruption of the BBB in patients presenting with acute stroke is common in patients with DM and is related to outcome. Methods: Sixty-two consecutive patients with ischemic stroke in the middle cerebral artery territory were enrolled within 3-7 days after onset. In ischemic lesion, BBB disruption was detected by parenchymal enhancement (PE) on 5 min delayed post-contrast T1 weighted imaging. National Institute of Health Stroke Score (NIHSS) assessed neurologic impairment on admission. Clinical outcome at 3 months was classified as unfavorable if the modified Rankin scale was >1. The independent factors associated with clinical outcome were analyzed using multivariate logistic regression analysis and OR with its 95% CIs were estimated. Results: An unfavorable stroke outcome was found in 19 diabetic patients and 21 non-diabetic patients. Diabetic patients had a significantly higher frequency of PE than non-diabetic patients (58.6 vs. 27.3%, p = 0.013) and DM was independently associated with PE (OR 4.40; 95% CI 1.22-15.83; p = 0.023). PE was significantly more common in diabetic patients with unfavorable stroke outcome (73.7%) than in other 3 subgroups: diabetic patients with favorable stroke outcome (30.0%), non-diabetic patients with favorable stroke outcome (38.1%) and unfavorable stroke outcome (8.3%; p = 0.002). PE was independently associated with unfavorable outcome (UO) in diabetic stroke (DS; OR 7.04; 95% CI 1.20-41.52; p = 0.031). Admission NIHSS score was associated with UO in non-DS (NDS) (OR 1.71; 95% CI 1.10-2.66; p = 0.017). Conclusions: Compared with NDS, DS had increased BBB disruption defined by the presence of PE. A different form of the relationship between admission NIHSS and UO in NDS, BBB disruption was related with UO in diabetic patients after stroke.