This study reports on cervical magnetic resonance imaging (MRI) performed in the fully flexed position in 13 male patients with Hirayama disease and 12 normal controls (males). The anterior-posterior diameter of the cervical cord at the superior margin of the C6 vertebral body was measured, as well as the angle between adjacent cervical bodies. Localized lower cervical-cord atrophy, cord flattening and abnormal signals in the posterior epidural space were studied. Patients demonstrated an increased angle between C5 and C6, and C6 cord lesions. There were significant differences between patients and controls in localized lower cervical-cord atrophy and cord flattening. Many patients were found to have a crescent-shaped high-intensity mass on T2WI MRI and a low-intensity mass on T1WI MRI in the posterior epidural space. In patients, there were specific imaging features of Hirayama disease on fully flexed MRI. Cervical MRI in the fully flexed position has significant value in the clinical diagnosis of Hirayama disease.