A patient, 30-year-old man, was admitted to Shinshu University Hospital with gait disturbance and numbness of both arms and legs in June 1985. General physical findings were normal except for facial asymmetry, i.e. mild right facial hemiatrophy. Blood pressure was normal and there were no signs of arteriosclerosis. Neurological examination revealed marked bilateral pyramidal tract signs, muscular weakness of all extremities predominant of the right side, spastic gait and sensory disturbance with impairment of pin prick and light touch sensation in the second and third trigeminal nerve regions and extremities of the left side, and mild loss of vibratory sense and numbness in all extremities. X-ray examination of the cervical spine and the myelogram of the spinal canal were normal. CT scan of the brain performed 3 hours after the myelography showed that the left vertebral artery extended from the left side of the medulla oblongata to the midline and distorted it by compression. MRI confirmed the findings of the CT scan. Vertebral angiography disclosed that the elongated left vertebral artery crossed the ventral aspect of the medulla oblongata. Compression of the medulla oblongata by the vertebral artery was diagnosed and neurovascular decompression was performed. About one month after the operation his spastic gait and muscular weakness were slightly improved, but these symptoms progressed thereafter. One year after operation his spastic gait was more marked than preoperatively. In many cases with dolichoectatic intracranial arteries, hypertension and arteriosclerosis have been reported to be usually associated with this condition. In other opinions dolichoectasia has been suggested to be a congenital disease, because such vessels are occasionally present in children.(ABSTRACT TRUNCATED AT 250 WORDS)