Objective: To explore the mid- to long-term effect of Wallis interspinous dynamic stabilization system on the adjacent segment degeneration. Methods: From March 2009 to June 2010, in Department of Orthopedics, Beijing Luhe Hospital, Capital Medical University, 24 patients with L4-5 monosegmental lumbar disc herniation were treated with posterior lumbar decompression combined with Wallis interspinous dynamic fixation. Clinical outcomes were evaluated with visual analogue score (VAS) (back pain), VAS (leg pain) and oswestry disability index (ODI) score. Intervertebral disc height (IDH) and range of motion (ROM) of the upper and lower adjacent segments were measured on X-ray. The degneration of lumbar intervertebral disc was evaluated on MRI. paired-t test was used to compare preoperative VAS, ODI, IDH, ROM and the degeneration of lumbar intervertebral disc with those at the final follow-up. Results: Twenty patients had a mean follow-up time of (65.2±4.7) months. At the final follow-up, VAS (back pain), VAS (leg pain) and ODI showed significant improvement (all P<0.01). At the final follow-up, IDH of the upper and lower adjacent segment showed no significant difference compared with those preoperatively (P>0.05); ROM of the upper adjacent segment increased (P<0.05), while ROM of the lower adjacent segment did not change significantly compared with that preoperatively (P>0.05). The degeneration of intervertebral discs at the upper and lower segments showed no significant changes at the final follow-up (P>0.05). Conclusions: Posterior decompression combined with Wallis interspinous dynamic stabilization system for monosegmental lumbar disc herniation can achieve satisfactory clinical results. More than five years' follow-up confirmed that the Wallis system will not accelerate adjacent segment degeneration.