PURPOSE: To determine the rate of and risk factors for 30-day unplanned admissions following hip arthroscopy in a U.S. METHODS: Patients undergoing hip arthroscopy were identified in the American College of Surgeons National Surgical Quality Improvement Program database using validated Current Procedural Terminology and International Classification of Diseases, Ninth Revision and Tenth Revision codes. Patient demographics, comorbidities, preoperative laboratory values, surgical details, and postoperative outcomes were compared between patients with unplanned admissions and those without. Univariate analysis comparing study cohorts was performed using 2-tailed Student t tests with Levene's test for equality of variance or χ2/Fisher exact tests as appropriate. Using variables that were significant in the univariate analysis, we created Cox proportional hazard models to identify independent predictors for unplanned admission. RESULTS: A total of 1931 cases of hip arthroscopy were identified. There were 18 cases of unplanned admissions within 30 days of index procedure (0.9%). The median time to unplanned admission was 14.5 days (interquartile range: 3.875-25.125 days). The most common reasons for admission were surgical-site infection (11.1%), wound complications (11.1%), and thromboembolic events (11.1%). There were 4 patients who required reoperation (22.2%). There were 7 cases (39.0%) that were readmitted for reasons unrelated to the index hip arthroscopy procedure. Multivariate analysis identified increasing body mass index, chronic corticosteroid use, and perioperative blood transfusion as factors independently associated with increased risk for unplanned admission. CONCLUSIONS: There exists a low incidence of 30-day unplanned admission, predominantly secondary to surgical-site infections, wound complications, and thromboembolic events. Independent risk factors for unplanned admission include greater body mass index, chronic corticosteroid use, and perioperative transfusions. LEVEL OF EVIDENCE: Level III Retrospective Cohort Study.