Objective：To investigate the role of electrophysiological test and MRI in the diagnosis of Hirayama disease. Methods：Ｃlinical features，electrophysiological characteristics and MRI findings of 14 patients with Hirayama disease were retrospectively re－viewed. Results：All symptomatic upper limbs had normal sensory nerve conduction velocity and motor nerve conduction velocity in the median and ulnar nerves. Compound motor active potentials（CMAPs） were normal in median nerve. Ulnar nerve CMAPs were de－creased by 20% of the normal value in 8 patients. Fourteen patients had neurological damage in muscles innervated by lower cervi－cal anterior horn cells（C7-8，T1） in the symptomatic limbs. Four patients had neurological damages in the symptomatic upper limbs. Seven patients had neurological damages in both upper limbs. Three patients had diffused neurological damages. No abnormality was observed in 10 patients according to MRI of cervical vertebra at normal physiological position. Four patients had atrophy of the cervi－cal and thoracic spinal segments. MRI of cervical vertebra at head-down position indicated anterior displacement of dura mater in the cervical and thoracic spinal segments in 14 patients with spinal cord being compressed and atrophic. Conclusions：Most patients with Hirayama disease have anterior horn damage in the lower cervical spinal segment on electromyography. Electrophysiological exam is important in the diagnosis of Hirayama disease. Diffused neurological damage could also be noticed in patients with Hiraya－ma disease. All patients with suspected Hirayama disease should have MRI scan of the cervical spinal cord at both normal physiological position and head-down position.