PURPOSE: We estimated the rate of unplanned hospital and intensive care unit (ICU) admissions following ambulatory surgery centre (ASC) procedures, and identified factors associated with their occurrence. METHODS: This retrospective cohort included adult patients who underwent ASC procedures within a large community practice from January 2010 to December 2014. Patients were categorized into two groups: unplanned postoperative hospital/ICU admission within 24 hr of procedure or uneventful discharge. Demographics, comorbidities, anesthesia type, procedure type, procedure group, and ASC facility were assessed. RESULTS: Of the 211,389 patients included, there were 211,147 uneventful discharges (99.89%) and 242 unplanned hospital admissions (0.11%), of which 75 were ICU admissions (0.04%). The multivariable logistic regression model for hospital admission showed an increased risk associated with age > 50 yr (odds ratio [OR], 1.53); American Society of Anesthesiologists (ASA) physical status (III vs II: OR, 1.45; IV vs II: OR, 1.88), comorbidity (chronic obstructive pulmonary disease: OR, 2.63; diabetes mellitus: OR, 1.62; transient ischemic attack: OR, 2.48) procedure (respiratory: OR, 2.92; digestive: OR, 2.66; musculoskeletal system: OR, 2.53), anesthetic management (general anesthesia [GA] and peripheral nerve block vs GA: OR, 1.79), and ASC facility (189BB: OR, 2.29; 30E9A: OR, 7.41; and BD21F: OR, 1.69). The multivariable logistic regression model for ICU admission showed increased risk of unplanned ICU admission associated with ASA physical status (ASA III vs II: OR, 3.0; ASA IV vs II: OR, 8.52), procedure (musculoskeletal system: OR, 2.45), and ASC facility (00E6C: OR, 3.14; 189BB: OR, 2.77; 30E9A: OR, 2.59; and BD21F: OR, 3.71). CONCLUSION: While a small percentage of adult patients who underwent ASC procedures required unplanned hospital admission (0.07%), approximately one-third of these admissions were to the ICU (0.04%). Facility was at least as strong a predictor of hospital admission as the patient- and/or procedure-specific variables.