As measures for the severity of carotid atherosclerosis, we compared common carotid artery (CCA) intima-media thickness (IMT) and plaque score (PS) for risk assessment of respective stroke subtypes. The subjects comprised 792 nonstroke and 311 stroke patients, including 72 with atherothrombotic infarction (AI), 113 with lacunar infarction (LI), 54 with cardioembolic infarction and 29 with cerebral hemorrhage. IMT was bilaterally measured on CCA far walls, and averaged. PS was obtained by summing up the maximum thickness of all plaques in bilateral carotid arteries. Both IMT and PS were greater in AI and LI patients than in nonstroke patients (all p < 0.05), but similar between other subtype and nonstroke patients. By receiver operating characteristic (ROC) curve analyses, both measures discriminated the likelihood for AI and LI (all p < 0.05), but not for other subtypes. When discriminating AI, ROC area defined by PS (0.80) was greater than that defined by IMT (0.68) (p < 0.05). Thus, although both CCA IMT and PS appear to help for risk assessment of AI and LI, risk of AI may be more effectively assessed by PS.