A prospective 3-year randomized study comparing conservative and surgical treatment of spondylotic cervical myelopathy to establish predictive factors for outcome after conservative treatment and surgery. The clinical, electrophysiological and imaging parameters were examined to reveal how they characterized the clinical outcome. The patients with a good outcome in the conservatively treated group were of older age before treatment, had normal central motor conduction time (CMCT), and possessed a larger transverse area of the spinal cord. The patients with a good outcome in the surgically treated group had a more serious clinical picture (expressed in mJOA score and slower walk). Patients should rather be treated conservatively if they have a spinal transverse area larger than 70 mm2, are of older age and have normal CMCT. Surgery is more suitable for patients with clinically worse status and a lesser transverse area of spinal cord.