Here we report a 47-year-old man with dissecting aneurysm of the basilar artery who developed Foville's syndrome due to upper pons involvement. At first he had an abrupt onset of dysarthria and weakness in his left upper and lower extremities during his work. Neurological examination on admission revealed mild disturbance of consciousness, absent light reaction on the left side, hypesthesia of the left face, absent gag reflex, dysarthria, and left hemiparesis with ataxia. On the second hospital day he developed paralysis of conjugate eye movement to the right, left central facial palsy, and left hemiplegia, and hyperhidrosis of the left side of the body. He was diagnosed to have superior pons type of Foville's syndrome. Computed tomography showed low density area in the right upper pons, and the basilar artery had marked lateral shift, dilatation, and calcification. Vertebral angiography demonstrated dissecting aneurysm of the basilar artery. Although it is very rare that dissecting aneurysm of the basilar artery causes the brain stem symptoms, its possibility should be considered when computed tomography shows marked lateral shift, dilatation, and/or calcification of the basilar artery.