Retrospective study to correlate classification of somatosensory-evoked potentials (SEPs) with symptomatic progress of patients with mild cervical spondylotic myelopathy (CSM). The aim of this study was to evaluate the usefulness of SEPs for predicting symptomatic progress of mild CSM. SEPs have been used for clinical diagnosis and intraoperative neuromonitoring in patients with CSM. However, the prognostic value of SEPs in predicting the progression of CSM remains unclear. A total of 200 patients with a clinical diagnosis of mild CSM were enrolled between September 2014 and February 2018. All patients received clinical assessment with the modified Japanese Orthopedic Association scale (mJOA), magnetic resonance imaging, and SEP tests in the first clinical visit and at 1-year follow-up. A classification of upper and lower limbs SEP was developed. At 1-year follow-up, patients with symptom decline >2 points in mJOA were considered progressive myelopathy cases. The relationship of progressive myelopathy and classifications of SEP was investigated. Fifty-four of 200 cases presented with progressive myelopathy. The incidence of progressive myelopathy was 2.6%, 27.7%, 23.8%, 86.7%, and 100% in Class I, II, III, IV, and V of upper SEPs, respectively, and 18.8%, 39.4%, 42.3%, and 62.5% in Class I, II, III, and IV of lower SEPs, respectively. For the combination classification of upper and lower SEPs, the incidence of progressive myelopathy was 0%, 13.7%, 24.3%, 91.1%, and 100% in Class I, II, III, IV, and V, respectively. There was a significant correlation of the incidence of progressive myelopathy with SEP classification for the upper SEPs (r = 0.94, P < 0.01) and the combination SEPs (r = 0.95, P < 0.01). The incidence of progressive degenerative myelopathy increased with the upper and combination SEP classifications. Thus, classification of SEPs could predict the clinical decline in mJOA in CSM, reflecting the probability of worsening of myelopathy. 4.