A prospective, randomized clinical study was performed to determine whether unilateral pedicle screw fixation was comparable with bilateral fixation in 1- or 2-segment lumbar interbody fusion. One hundred eight patients with lumbar degenerative diseases were randomly assigned to the unilateral (n=56) or bilateral (n=52) pedicle screw fixation group. Interbody fusion was performed in 1 or 2 levels with 1 cage. Operative time, blood loss, duration of hospital stay, functional outcome, fusion rate, and complication rate were recorded and compared statistically. The patients were followed for 3 years postoperatively.Successful radiographic fusion was documented in all patients. No flexion-extension hypermobility or pedicle screw loosening or breakage occurred during the follow-up period. No significant difference existed between the 2 groups when comparing the union rate, complication rate, and functional outcome scores (P>.05). However, compared with the bilateral pedicle screw group, a significant decrease occurred in operative time, duration of hospital stay, and blood loss in the unilateral group (P<.01). Unilateral pedicle screw fixation was as effective as bilateral fixation when performed in addition to 1- or 2-level lumbar interbody fusion. The authors recommend the use of unilateral fixation in lumbar interbody fusion with 1 cage for lumbar degenerative diseases without major instability.