BACKGROUND: Criteria to decide whether carotid endarterectomy (CEA) or carotid artery stenting (CAS) is the best mode of therapy in a specific case of cervical carotid stenosis have not been established. Overall, recent randomized clinical trials have reported that the effect on the prevention of stroke is not significantly different between CEA and CAS. CEA is more appropriate than CAS for soft atherosclerotic plaques, since such soft plaques are associated with a high incidence of ischemic complications during CAS. Therefore identification of the plaque type with noninvasive preoperative examinations plays an important role for selecting the suitable surgical method, CEA or CAS. OBJECTIVE: The objective of this study was to evaluate the association among findings of carotid ultrasonography (carotid US), black blood magnetic resonance imaging (BB-MRI), and the histopathological findings of plaque specimens removed during CEA, and secondly to consider whether these diagnostic tools are useful to predict the characteristics of carotid plaques. METHOD: We investigated a total of 25 consecutive patients who underwent CEA from November 2008 to June 2010 at Kyoto Medical Center. We examined carotid plaque in 17 patients employing both carotid US and BB-MRI, 7 patients by carotid US, and 1 patient by BB-MRI. The plaque echogenicity was qualitatively assessed as low, intermediate, or high, and the MR signal intensity of the carotid plaque was classified as low or high compared with the intensity of the ipsilateral sternocleidomastoid muscle. The plaque specimens were macroscopically and pathophysiologically classified as soft or hard plaque. RESULTS: All low-echogenic plaques on carotid US were histologically soft plaques. The high-intensity plaques on T1-weighted imaging (T1WI) showed a tendency toward soft plaque. Thirteen of 14 plaques with high signal intensity on T1WI were morphologically soft. Eleven of 14 plaques with an intermediate echogenicity on carotid US were also morphologically soft. CONCLUSION: The findings of carotid ultrasonography and BB-MRI are closely associated with the CEA specimen's morphology. Ultrasonography alone is insufficient to diagnose the plaque type accurately in some patients. Employing both carotid US and BB-MRI is useful for evaluating the characteristics of carotid plaque.