Hirayama disease (HD) is a rare motor neuron disorder that involves a single upper extremity. It is clinically characterized by weakness and atrophy of the muscles of the hand and forearm. This article presents a 19-year-old woman who visited the orthopedics outpatient clinic with weakness and atrophy in her right hand and was clinically diagnosed with advanced stage carpal tunnel syndrome and scheduled for surgical intervention; she was later diagnosed with HD by an electrophysiological study. As a result, it has been found that a careful electrophysiological study and neurological examination can be used to diagnose HD. In this way, advanced stage carpal tunnel syndrome will be ruled out and patients will be spared from an unnecessary surgical operation.