Background: Literature is scarce regarding the influence of psychological readiness on return to sports after shoulder instability surgery. Purpose: To evaluate the predictive ability of the Shoulder Instability–Return to Sport after Injury (SIRSI) score in measuring the effect of psychological readiness on return to sports and to compare it between athletes who returned to sports and athletes who did not return to sports. Study Design: Cohort study; Level of evidence, 2. Methods: A prospective analysis was performed of patients who underwent an arthroscopic Bankart repair or a Latarjet procedure between January 2019 and September 2020. Psychological readiness to return to play was evaluated using the SIRSI instrument. Preoperative and postoperative functional outcomes were measured by the Rowe, Athletic Shoulder Outcome Scoring System, and Western Ontario Shoulder Instability Index scores. The predictive validity of the SIRSI was assessed by the use of receiver operating characteristic (ROC) curve statistics. The Youden index was calculated and used to determine a SIRSI score cutoff point that best discriminated psychological readiness to return to sports. A logistic regression analysis was performed to evaluate the effect of psychological readiness on return to sports and return to preinjury sports level. Results: A total of 104 patients were included in this study. Overall, 79% returned to sports. The SIRSI had excellent predictive ability for return-to-sport outcomes (return to sports: area under ROC curve, 0.87 [95% CI, 0.80-0.93]; return to preinjury sports level: area under ROC curve, 0.96; [95% CI, 0.8-0.9]). A cutoff level of ≥55 was used to determine whether an athlete was psychologically ready to return to sports and to return to preinjury sports level (Youden index, 0.7 and 0.9, respectively). Of those who returned to sports, 76.8% were psychologically ready to return to play, with a median SIRSI score of 65 (interquartile range, 57-80). In comparison, in the group that did not return to sports, only 4.5% achieved psychological readiness with a median SIRSI score of 38.5 (interquartile range, 35-41) ( P < .001). Regression analysis for the effect of SIRSI score on return to sports was performed. For every 10-point increase in the SIRSI score, the odds of returning to sports increased by 2.9 times. Moreover, those who did not achieve their preinjury sports level showed poorer psychological readiness to return to play and SIRSI score results. Conclusion: The SIRSI was a useful tool for predicting whether patients were psychologically ready to return to sports after glenohumeral stabilization surgery. Patients who returned to sports and those who returned to their preinjury sports level were significantly more psychologically ready than those who did not return. Therefore, we believe that the SIRSI score should be considered along with other criteria that are used to decide whether the patient is ready to return to sports.