The use of narrower window width settings on computed tomography (CT) improves sensitivity for detection of early ischemic changes in acute ischemic stroke. This study analyzed the effect of optimization of window settings on the accuracy of Alberta Stroke Program Early Computed Tomography Score (ASPECTS) performed on non-contrast CT (NCCT) and CT angiography source images (CTA-SI). ASPECTS was calculated on NCCT and CTA-SI with standard and optimized window width/center settings in a consecutive series of patients with acute ishcemic stroke. The difference between CT-based ASPECTS and ASPECTS performed on follow-up magnetic resonance imaging (MRI) were calculated to determine the disparity between initial estimates of the extent of ischemia on CT and follow-up lesion imaging by MRI. Forty-four patients were included into the study. The mean difference with respect to follow-up MRI-ASPECTS was 4.1 +/- 2.2 for standard NCCT-ASPECTS, 3.7 +/- 2.3 for optimized NCCT-ASPECTS, 3.0 +/- 2.2 for standard CTA-SI-ASPECTS, and 2.7 +/- 2.1 for optimized CTA-SI-ASPECTS. The improvement introduced by the optimization of window settings and use of CTA-SI was statistically significant (P < .01). Our data indicate that the accuracy of ASPECTS is improved with optimized window display settings. This improvement is irrespective of experience or specialty of the rater performing the assessment.