BACKGROUND AND PURPOSE: The apolipoprotein B (apoB)/apoAI ratio is recognized as a better indicator of cardiovascular disease than other cholesterol measures. Whether intracranial or extracranial atherosclerosis is more closely associated with an increased apoB/apoAI ratio has not been investigated. METHODS: A total of 464 statin or fibrate naïve Korean patients with acute ischemic stroke was categorized into 3 groups: intracranial (ICAS, n=236), extracranial (n=44), and no cerebral atherosclerotic stenosis (n=184). The apoB/apoAI ratio and demographics, including the presence of metabolic syndrome, were compared among the groups. RESULTS: The ICAS group showed a higher apoB/apoAI ratio (0.81±0.02) than both the extracranial atherosclerotic stenosis (0.74±0.03) and no cerebral atherosclerotic stenosis (0.72±0.02) groups (P=0.002). The ratio was substantially increased (0.93±0.03) in patients with advanced ICAS (≥3 intracranial stenoses). With a multivariable analysis, the highest apoB/apoAI ratio quartile was an independent predictor of ICAS (OR, 2.13; 95% CI, 1.05 to 4.33). A dose-response relationship was observed between the presence of advanced ICAS and the apoB/apoAI ratio quartiles (OR, 4.03; 95% CI, 1.26 to 12.88 for the second quartile; OR, 4.88; 95% CI, 1.54 to 15.49 for the third quartile; and OR, 7.79; 95% CI, 2.41 to 25.16 for the fourth quartile when referenced to the first quartile). Patients having more metabolic syndrome components were more likely to have ICAS, advanced ICAS, and a higher apoB/apoAI ratio (P<0.001 for all). CONCLUSIONS: A higher apoB/apoAI ratio is a predictor of ICAS rather than of extracranial atherosclerotic stenosis or no cerebral atherosclerotic stenosis. The apoB/apoAI ratio might be a biomarker for ICAS in Asian patients with stroke.