The relationship of the pelvis to the spine has previously been overlooked, and its importance in sagittal balance has been underestimated. Purpose: To evaluate the sagittal balance improvement in surgically treated patients with high grade Lytic Spondylolisthesis treated with PLIF and its relation to clinical outcome. Patient sample: Prospective case study of 30 patients with high grade Lytic Spondylolisthesis with follows up of at least 12 months. Methods: It consisted of a prospectively collected consecutive series of 30 patients with high grade Lytic Spondylolisthesis who met the inclusion criteria treated between September 2019 and August 2022. All cases were managed by posterolateral fusion (PLF) added to posterior interbody fusion (PLIF) in Cairo University hospital, and Alharam hospital. Results: All patients achieved satisfactory results as regards the back pain, radicular pain and neurologic deficits. ODI significantly improved from mean 69.37±5.49 SD to 10.97±2.14 at 12 months (P <0.001). Mean Back pain VAS decreased significantly from mean 7.76 ±0.71SD to 0.93±0.37 at 12 months (P <0.001). Fusion improved from mean 4.17±0.83 SD by 6th month to 4.70±0.60by one year. Two patients were complicated by dural tear (6.7%), two patients had superficial infection (6.7%) and three patients complicated delayed fusion (10%). None had undergone a revision surgery. Conclusions: Clinical outcomes are in direct relation to radiological outcome after sagittal balance correction using posterior fusion