We report on a patient with traumatic dissection limited to the basilar artery causing a locked-in syndrome. Magnetic resonance imaging (MRI) showed infarction of the basis pontis and a high signal intensity ring surrounding the central lumen of the basilar artery. Vertebral angiography revealed a double lumen within the basilar artery, consistent with a dissection. MRI and angiography are complementary to each other, and we consider both to be necessary for accurate diagnosis. Because MRI is less invasive than angiography, MR examinations should be performed before angiography for screening.