STUDY DESIGN: Retrospective cohort study. PURPOSE: The aim of our study is to evaluate the extent of posterior spinal dural shift following spinous process splitting multi-level intervertebral lumbar laminectomies, and determine the relationship between posterior spinal dural shift and preoperative parameters. OVERVIEW OF LITERATURE: There are no existing studies on the posterior spinal dural shift after spinous process-splitting multi-leveled lumbar laminectomies. METHODS: We examined 37 patients who underwent spinous process-splitting laminectomies in at least two intervertebral levels, including at the L5/S level. We defined the distance between the vertebral bodies and the anterior edge of the dural sac in the magnetic resonance images at the L5 vertebral level as the anterior dural space (ADS) and detected the difference (d-ADS) between preoperative ADS (pre-ADS) and postoperative ADS (post-ADS). We assessed the relationship between ADS or d-ADS, and preoperative parameters, including age, sex, lumbar lordosis, focal lordosis (FL), and number of decompression levels. RESULTS: Post-ADS was significantly greater than pre-ADS (p<0.001). Pre-ADS was significantly correlated with FL (p=0.44, p<0.01) and also with post-ADS (p=0.43, p<0.01). d-ADS was negatively correlated with pre-ADS (p=−0.37, p<0.05). A single regression analysis revealed that the relationship between d-ADS and pre-ADS was described as d-ADS=3.67−0.46×pre-ADS. In one of three patients whose d-ADS was above the range of two standard errors, reoperation was performed because of impingement of the nerve root caused by the excessive posterior dural shift. CONCLUSIONS: Posterior dural shifts occur after spinous process-splitting multi-level lumbar laminectomies, including at the L5/S level. FL and pre-ADS are good predictive factors for posterior dural shift. Excessive posterior dural shift may lead to stretching and impingement of nerve roots and thus require attention.