To evaluate the results of posterolateral fusion alone (66 patients) and combined posterolateral and anterior fusion (39 patients) in situ, 105 consecutive patients younger than 25 years of age with spondylolisthesis, retrospectively were examined clinically and radiologically. The follow-up rate was 98% after a mean of 8.2 years (range, 2.0-15.3). Pre- and postoperative progression of slip was rare (6% and 1%, respectively), and no prognostic factors were found. The definite pseudarthrosis rate was 6%. In patients with low- and high-grade slip, 67% and 88% (respectively) were satisfied at follow-up, suggesting that the indication for operative treatment in patients with low-grade slip is relative.