BACKGROUND Despite the recent trend toward outpatient orthopedic surgical procedures, there are patients who incur unanticipated conversions to inpatient status either immediately following ambulatory surgery or within days to weeks via presentation to the emergency department. The purpose of this study was to examine characteristics, co-morbidities, and causes of admissions in these populations in order to help identify factors for which strategies can be developed in order to minimize unanticipated admissions and medical costs. METHODS Using a major academic medical center's bill-ing department's database, 95 outpatients were identified who were immediately converted into inpatient status and another 84 outpatients who were admitted within 30 days of surgery. The reasons for admission, length of procedure, length of admission, ASA score, comorbidities, and insur-ance type were assessed. RESULTS For the patients who were converted to inpa-tient status postoperatively, pain accounted for 57% of conversions. Hypertension was the most commonly seen comorbidity (44%). In patients admitted within 30 days of ambulatory surgery, infection (25%) was the most common cause of admission. Smoking (46.4%) represented the most common comorbidity in this cohort. CONCLUSIONS The majority of immediate inpatient con-versions were due to pain, emphasizing the need to optimize perioperative analgesia and provide impactful patient education regarding postoperative pain expectations. For patients admitted within 30 days of surgery, infection represented the majority of readmissions, and smoking was the most common comorbidity. While, some infections may be unavoidable, this stresses the importance of medical and social factor optimization prior to surgery. Addressing these factors leading to unanticipated admissions can have a profound effect on health care expenditures and patient outcomes.