Sixty-seven patients with cervical spondylotic myelopathy treated with expansive laminoplasty were retrospectively reviewed at a minimum 2-year follow-up. This study was designed to evaluate whether preoperative instability influences the clinical outcome in patients with cervical spondylotic myelopathy treated with laminoplasty without spinal fusion. Patients with preoperative instability were older and had shorter durations of symptoms prior to surgery than those without the instability. There were no significant differences in prevalence of axial symptoms, neurologic recovery, or radiologic findings between patients with and without preoperative cervical instability. At follow-up, the cervical range of motion was limited to 43.5% of the preoperative range, and no cervical instability was observed in any patients. Preoperative instability does not influence the clinical outcome and can be ignored if expansive laminoplasty is indicated for patients with cervical spondylotic myelopathy.