OBJECTIVE: The purpose of the current study is to investigate the effect of the prosthetic disc nucleus replacement on the mobility and height of the intervertebral disc and adjacent segments. METHODS: Thirteen patients who underwent L4-L5 prosthetic disc nucleus replacement were included in this study. A retrospective review of clinical and radiological data was conducted. The L4-L5 disc height and sagittal rotation angle of L3-L4, L4-L5, L5-S1 were measured in the static and dynamic lateral radiographs pre- and postoperatively. RESULTS: There were seven men and six women whose mean age was 37 years(range, 24-49 years). The mean follow-up period was nine months(range, 6-14 months). In all cases the L4-L5 motion segment demonstrated angular motion between flexion and extension with a mean of 4degrees(+/-2.3degrees) of sagittal rotation angle. The disc height increased from preoperative levels by 117%. There was no difference in angular motion of adjacent segments between pre- and postoperative data. CONCLUSION: The prosthetic disc nucleus replacement after discectomy is shown to restore the disc height and maintain segmental mobility.