Thirteen patients with spondylolisthesis (six isthmic type and seven degenerative type) and ten patients with intervertebral disk herniation were treated by anterior lumbar interbody fusion. Preoperative and postoperative computed tomography (CT) scans were performed for each patient, and changes in anteroposterior (AP) diameter and lateral diameter of the dural sac, the area of the dural sac, and the amount of disk bulging were measured. The periodic tomogram was done in all patients postoperatively, and one- and two-year fusion rates were calculated. The calculations were compared with the early and late clinical results. The early clinical results after operation were excellent in 26.1%, good in 56.5%, and fair in 17.4%. The late clinical results were similar to early results. The early clinical results correlated with the changes in the spinal canal, such as an increase in AP diameter of the dural sac and a decrease in amount of disk bulging after anterior interbody fusion. There was statistical correlation between the early clinical results and the change in AP diameter of the dural sac. But the late clinical results were influenced by multiple factors including solid bony fusion.