In the present study, we report muscular atrophy of the right distal upper extremity in a 14-year-old boy. The disease progressed insidiously for about 2 years, and during our first examination, he exhibited weakness and wasting in the right hand, and paresthesia on the C6-8 dermatomal area in the right upper extremity. Electromyography revealed neurogenic changes in atrophic muscles. Conduction velocity of the ulnar nerve of the affected hand was decreased. Magnetic resonance imaging (MRI) of the cervical spine in the neutral position revealed focal spinal cord atrophy and a small area of high signal intensity at C5-6 level. In the flexion-induced cervical spine MRI scan, the spinal cord was noticed to be compressed by the posterior dural sac with a forward shift and flow voids in the epidural space. All these parameters led to the diagnosis of Hirayama disease (HD). This is the first report of HD in Korea by pediatrician, even though it is characterized by juvenile onset.