STUDY DESIGN: A retrospective review of prospectively collected registry data. OBJECTIVES: (1) Examine functional outcomes of patients with postoperative sacral slope (SS)<30 degrees versus SS≥30 degrees after single-level transforaminal lumbar interbody fusion (TLIF) for degenerative spondylolisthesis (DS); (2) determine the factors associated with SS at the last follow-up. SUMMARY OF BACKGROUND DATA: Few studies have examined the relationship between spinopelvic parameters and functional outcomes in patients with DS undergoing short-segment TLIF. Although SS of 30 degrees has been proposed as the ideal spinopelvic parameter for eliminating residual pain and disability in adult spinal deformity, the ideal value for DS remains unknown. METHODS: Prospectively collected registry data of 63 patients who underwent single-level L4-L5 open TLIF with sagittal realignment for DS were reviewed. Pelvic incidence, lumbar lordosis (LL), pelvic tilt, SS, listhesis excursion, and Bridwell fusion grading were recorded. Patients were stratified into SS<30 degrees (n=26) or SS≥30 degrees (n=37) at the last follow-up. All patients were assessed preoperatively and postoperatively at 2 years. Receiver operating characteristics curve analysis was used to assess the relationship between expectation fulfillment and change in SS. RESULTS: Patients with SS≥30 degrees had significantly lower back pain at 2 years (P<0.04). There were no differences in leg pain or outcome scores (Oswestry Disability Index, Short-Form 36 Physical, and Mental Component Summaries), although there was a trend towards better outcomes and higher satisfaction/expectation fulfillment in patients with SS≥30 degrees. The SS≥30 degrees group had a higher preoperative LL (P=0.04) and SS (P<0.01). Preoperative SS was correlated with SS (R=0.71, P<0.01) and LL (R=0.51, P<0.01) at the last follow-up. The area under the curve for change in SS was 0.680 (95% confidence interval, 0.453-0.907) for predicting expectation fulfillment at 2 years. CONCLUSIONS: Patients with increased SS (≥30 degrees) experienced less back pain after short-segment lumbar fusion surgery. This was associated with increased LL postoperatively, indicating better sagittal balance.