Objectives: Return to the Emergency Department (ED) within 90-days following arthroscopic shoulder surgery represents a potential source of increased healthcare expenditures. Understanding the risk factors could bring about interventions aimed at reducing its prevalence. Methods: A retrospective review of all shoulder arthroscopies undertaken at a single academic institution from February 2016 through November 2023 was performed. Patient demographics and surgical data, including age, diagnosis of mental health disorder, history of priorAipsi- Aand/or contralateral shoulder arthroscopy, body mass index (BMI), smoking status, age-adjusted Charlson Comorbidity Index (ACCI), operative time and nature of the surgical procedure was collected. Patient visits to the ED within 12 months prior to surgery were recorded. Regression analysis was utilized to determine the independent predictors for 90-day postoperative ED return. Results: There were 584 total cases included in this study, of which 303 (52%) were women. ATheAmedian age of the cohort was 57 years (IQR 51,62). There were 60 (10.3%) patients who experienced at least one unplanned 90- day ED return visit. A diagnosis of mental health disorder (OR 2.67, 95% CI 1.50-4.75, P=0.001), an ED visit within 3 months of surgery (OR 2.63, 95% CI 1.28-5.40, P=0.009), an ED visit between 3-6 months of surgery (OR 2.79, 95% CI 1.41-5.54, P=0.003), and an ED visit between 6-12 months of surgery (OR 1.98, 95% CI 1.07-3.66, P=0.029) was significantly associated with a 90-day unplanned postoperative ED visit. Finally, having >3 preoperative ED visits was significantly associated with a 90-day postoperative ED visit (OR 9.41, 95% CI 3.68-24.06, P<0.001). Conclusion: Patients with a history of mental health disorder and those with a visit to the ED within 12 months prior to the planned shoulder arthroscopy should be counseled preoperatively regarding appropriate direct contact with the treating surgical team following discharge to minimize postoperative 90-day ED visits. Level of evidence: III