BACKGROUND: Postoperative changes in lumbar lordosis (LL) after transforaminal lumbar interbody fusion (TLIF) and the related factors are not well-understood. Recently, the preoperative difference in LL between standing and supine positions (DiLL) was proposed as a factor for predicting postoperative radiologic outcomes after short-segment TLIF. This study investigated the influence of DiLL on mid-term radiological outcomes after short-segment TLIF. METHODS: Sixty-six patients with lumbar degenerative disease treated with short-segment TLIF (1-2 levels) who underwent lumbar spine standing radiographs at 3 months, 6 months, 1 year, 2 years, 3 years, 4 years, and 5 years postoperatively were divided into DiLL (+) and DiLL (-) groups (preoperative DiLL ≥0° and <0°, respectively). Associations between the postoperative change in LL and DiLL and clinical outcomes (Oswestry disability index (ODI) and Nakai score) were evaluated. RESULTS: Temporary restoration of LL (+4.5°) until 1 year postoperatively and a subsequent decrease in LL from 1 to 5 years postoperatively (-5.3°) was observed in the DiLL (+) group. No postoperative change in LL was observed in the DiLL (-) group. Postoperative changes in LL were mainly observed in non-fused segments. The postoperative change in LL (ΔLL) until 1 year postoperatively had a significant positive association with DiLL (p = 0.00028), whereas ΔLL from 1 to 5 years postoperatively showed a significant negative association with DiLL (p = 0.010) and a positive association with Nakai score (p = 0.028). ΔLL until 5 years postoperatively showed a significant positive association with postoperative ODI improvement (p = 0.011). CONCLUSIONS: DiLL (+) patients showed a specific time course with temporary LL restoration until 1 year postoperatively and a subsequent decrease in LL from 1 to 5 years postoperatively. Patients with larger postoperative increase in LL until 5 years postoperatively and lesser decrease in LL from 1 to 5 years postoperatively tended to show better mid-term clinical outcomes.