The aim of this prospective randomized study was to compare the radiological and clinical outcome after treatment of lumbar spinal stenosis L4L5 with or without spondylolisthesis, with either posterior lumbar interbody fusion (PLIF) (26 patients) or Dynesys posterior stabilization (27 patients). Demographic characteristics were comparable in both groups. Dynesys stabilization resulted in significantly higher preservation of motion at the index level (p < 0.001), and significantly less (p < 0.05) hypermobility at the adjacent segments. Oswestry Disability Index (ODI) and VAS for back and leg pain improved significantly (p < 0.05) with both methods, but there was no significant difference between groups. Operation time, blood loss, and length of hospital stay were all significantly (p < 0.001) less in the Dynesys group. The latter benefits may be of particular importance for elderly patients, or those with significant comorbidities. Complications were comparable in both groups. Dynesys posterior stabilization was effective for treating spinal stenosis L4L5 with or without spondylolisthesis.