Abstract: Purpose: High-grade isthmic spondylolisthesis (HGISL) is a severe condition, associated with low-back pain (LBP) and radiculopathies. The present study is a monocentric prospective observational study investigating the clinical-radiological outcomes of a bilateral minimally invasive TLIF (bm-TLIF) for HGISL. Material and Methods: Patients who underwent bm- TLIF for HGISL at our institution, were considered for inclusion. Clinical-radiological outcomes and complications were collected. Results: Twenty-one patients (14M:7F) were included and the mean clinical follow-up (FU) time was 27(±6) months. There was a significative improvement of the mean VAS-back, VAS-legs, ODI, and SF-36 PCS scores, comparing pre- and last FU measurements. The mean pelvic tilt (p0,05). The univariate analysis showed that residual slip angle (> or 10°) may independently influence VAS-b (p