Background: The Degenerative lumbar Spondylolisthesis Instability Classification (DSIC) system categorizes spondylolisthesis (stable, potentially unstable, unstable) based on surgeon impression. It does not contain objective criteria. Objective-1: Develop a quantitative-DSIC system from predetermined radiographic/clinical variables. Objective-2: Compare qualitative (surgeon-assigned) and quantitative (objective) DSIC Types. Objective-3: Determine proportion of patients receiving more invasive surgery than warranted based on the objective system. Methods: Patients from 8 centers were enrolled prospectively (2015–2020). Radiographic/clinical variables were collected and included/excluded from the quantitative DSIC system based on prior systematic review. Scores were converted to DSIC Types: 0-2 points (“Stable”; Type 1), 3 points (“Potentially Unstable”; Type 2), 4-5 points (“Unstable”; Type 3). Surgical procedures performed were compared to those suggested by the objective system. Results: Quantitative DSIC scores were calculated (309 patients). The score includes five variables: facet effusion, disc height, translation, disc angle, and low back pain. Quantitatively, 57% were stable, 34% potentially unstable, and 9% unstable patients. Qualitatively, 30% were stable, 53% potentially unstable, and 17% unstable patients. Surgeons assigned more instability than the objective scoring system in 42% of cases. More invasive surgery was performed in 57% of cases. Conclusions: Surgeons are more likely to categorize greater degrees of spinal instability than what is objectively scored.