METHODS The correlation between preoperative and postoperative lateral functional radiograms and clinical results was analyzed in 74 cases of myelopathy treated by anterior cervical fusion. OBJECTIVE To clarify the correlation between clinical results and radiologic findings (developmental and dynamic stenosis). BACKGROUND Although radiologic changes have been reported at the disc level adjacent to anterior cervical fusion, the question of whether these radiologic findings affect the clinical results of anterior fusion has not been resolved. METHODS The "deteriorated" results group (28 cases) was composed of cases with deterioration of 2 points or more in the Japan Orthopedic Association score at follow-up compared with the postoperative best score. The "good" results group (46 cases) exhibited a recovery rate of > or = 50%. The two groups were compared in lateral functional roentgenograms on which the sagittal canal diameter in each vertebra and the diameter between the inferoposterior lip of the vertebral body and the anterior margin of the lamina of the distal vertebra in the extended neck were measured. A diameter of less than 12 mm was defined as developmental canal stenosis or dynamic canal stenosis. RESULTS Fifty-four percent of the cases in the deteriorated results group had developmental canal stenosis, whereas the same findings were identified in only 2% of the cases in the good results group (P < 0.01). Preoperative dynamic canal stenosis at the disc level adjacent to the fusion was found in 64% of the patients in the deteriorated results group and in only 4% of the patients in the good results group (P < 0.01). CONCLUSIONS Patients in the deteriorated results group showed a higher incidence of preoperative developmental and/or dynamic canal stenosis at the adjacent disc level than those in the the good results group. These results indicate that patients with preoperative developmental canal stenosis are not suitable candidates for anterior cervical fusion. When dynamic canal stenosis is found below or above the level of fusion, simultaneous fusion is recommended to avoid deterioration of the myelopathy.