Recently spinal degeneration disease and spinal surgery for elderly patients is increasing. It may increase the incidence of postoperative dementia and delirium in elderly patients compared to that of younger ones. The present study was designed to examine the risk factors for dementia and delirium after spinal surgery in elderly patients. We studied 39 patients who had spinal surgery aged greater than 70 years. We retrospectively studied about age, duration of anesthesia, duration of bed rest, and past history. The incidence of postoperative dementia was 9 (23.1%) and delirium was 2 (5.1%). Delirium was improved after leaving the bed, but 8 patients however had dementia which lasted until time of discharge, many of which developed a tendency to improve after that time. Patients who had postoperative dementia or delirium tended to have a diabetes mellitus and significantly longer length of stay in bed at the preoperative stage due to paresis from spinal cord injury. These results suggested that age, diabetes mellitus, bedridden to be important factors in postoperative dementia and delirium.