We studied six patients with basilar artery occlusion using magnetic resonance imaging. Two patients also had arteriography. All had signs consistent with pontine infarction; three had a "locked in" syndrome. Magnetic resonance imaging (five done within 24 h of onset of progression of neurologic symptoms) revealed a linear structure of increased signal intensity in the pontine cistern on T1-weighted parasagittal images and absence of flow void phenomena. Hyperintense signals at various brain stem levels corresponding to the course of the basilar artery were noted on T2-weighted images. Multiple parenchymal abnormalities were noted in the brain stem (six), cerebellum (four), occipital lobes (two), and thalamus (two). Magnetic resonance performed early in the course of basilar artery occlusion is a high-yield, safe procedure and might eliminate the need for arteriography.