The aim of this study was to examine and characterize the reversibility of the cervical somatosensory electrophysiological pathways during neutral and flexed neck positions. The parameters of somatosensory evoked potentials (SEPs) during neutral and flexed neck positions (N9, N13, and N20 SEP latencies; N9-N13 and N13-N20 inter-peak latencies; and the changes in N9-N13 and N13-N20 inter-peak latency during neutral and flexed neck positions) were measured in the patients with Hirayama disease (HD) and also in the healthy controls. In patients with HD, there was a significant difference in the mean value of N13-N20 inter-peak latency during the flexed neck position compared to that of the healthy controls (p < 0.05). In a multivariate logistic regression analysis, N13-N20 inter-peak latency during the flexed neck position significantly correlated with the presence of HD (p < 0.05). Collectively, in this cohort of patients with HD, the neck flexion of patients with HD showed a reversible effect on the SEP parameter, especially in N13-N20 inter-peak latency. Conventional diagnosis of HD is based on nerve conduction studies and electromyography along with a cervical flexion MRI, and our study suggests the possibility of an additional and cost-effective electrophysiological marker that may be helpful in the diagnosis of HD.