OBJECTIVE Extensive cervical laminectomy has been widely used in the treatment of progressive myelopathies secondary to stenotic conditions. Complications of this procedure such as spinal instability, accelerated spondylotic changes, postoperative spinal deformity and constriction of the dura mater by extradural scar tissue formation have been recognized. However, the frequency of these complications is probably overestimated and their consequences on the clinical outcome remain unknown. The purpose of this report was to describe the incidence and consequences of cervical spinal deformity and instability after multilevel laminectomy in adult patients with myelopathy caused by cervical spondylosis and to determine the usefulness of preoperative dynamic films in the prevention of postoperative destabilization. METHODS 30 patients older than 30 years who underwent a laminectomy of more than 3 levels without fusion for myelopathy secondary to cervical spondylosis were reviewed retrospectively with an average follow-up of 5 years. Functional results were evaluated according to the Japanese Orthopaedic Association scoring system. Lateral views in neutral position, in flexion and in extension of the preoperative cervical roentgenograms were analyzed in comparison with the last follow-up one in order to identify the changes in the curvature of the cervical column, in the range of motion of the neck, in the intervertebral angular mobility and antero-posterior displacement of the vertebral bodies, and finally to identify the incidence of spinal instability. RESULTS 18 patients (31 per cent) developed postoperative changes in cervical spine curvature. 15 patients (25 per cent) had one or more destabilized levels. Deformities of the cervical spine occurring after surgery do not appear to cause any symptom or neurologic abnormalities. Destabilization required repeat surgery in 3 patients. All the levels found destabilized on the postoperative films were hypermobile on the preoperative dynamic radiographs. A preoperative olisthesis without hypermobility was not a risk factor for postoperative destabilization. CONCLUSIONS The use of preoperative dynamic radiographs should improve the selection of patients undergoing laminectomy for the treatment of multilevel cervical cord compression. Dynamic X-rays may also reinforce the need for possible adjunctive procedures such as fusion and instrumentation, in order to prevent a postoperative destabilization. A preoperative olisthesis with a hypermobility in sagittal or horizontal planes must be fused and instrumented.