IMPORTANCE: The Instability Severity Index (ISI) score was developed to evaluate a patient's risk of recurrent shoulder instability following arthroscopic Bankart repair. While patients with an ISI score of >6 were originally recommended to undergo an open procedure (ie, Latarjet) to minimise the risk of recurrence, recent literature has called into question the utility of the ISI score. OBJECTIVE: The purpose of this systematic review was to evaluate the efficacy of the ISI score as a tool to predict postoperative recurrence among patients undergoing arthroscopic Bankart procedures. EVIDENCE REVIEW: Articles were included if study participants underwent arthroscopic Bankart repair for anterior shoulder instability and reported postoperative recurrence by ISI score at a minimum of 2 years of follow-up. Methodological study quality was assessed using the Methodological Index for Non-Randomized Studies criteria. Pearson's χ2 test was used to compare recurrence rates among patients above and below an ISI score of 4. Sensitivity, specificity, mean ISI scores and predictive value of individual factors of the ISI score were qualitatively reviewed. FINDINGS: Four studies concluded the ISI score was effective in predicting postoperative recurrence following arthroscopic Bankart repair; however, these studies found threshold values lower than the previously proposed score of >6 may be more predictive of recurrent instability. A pooled analysis of these studies found patients with an ISI score <4 to experience significantly lower recurrence rates when compared with patients with a score ≥4 (6.3% vs 26.0%, p<0.0001). The mean ISI score among patients who experienced recurrent instability was also significantly higher than those who did not. CONCLUSIONS AND RELEVANCE: The ISI score as constructed by Balg and Boileau may have clinical utility to help predict recurrent anterior shoulder instability following arthroscopic Bankart repair. However, this review found the threshold values published in their seminal article to be insufficient predictors of recurrent instability. Instead, a lower score threshold may provide as a better predictor of failure. The paucity of level I and II investigations limits the strength of these conclusions, suggesting a need for further large, prospective studies evaluating the predictive ability of the ISI score. LEVEL OF EVIDENCE: IV.