Care for patients undergoing ambulatory procedures is a broad and expanding area of anesthetic and surgical practice. There were over 35 million ambulatory surgical procedures performed in the US in 2006. Ambulatory procedures are diverse in both type and setting, as they span the range from biopsies performed under local anesthesia to intra-abdominal laparoscopic procedures, and are performed in offices, freestanding ambulatory surgery centers, and ambulatory units of hospitals. The information on adverse events from these varied settings comes largely from retrospective reviews of sources, such as quality-assurance databases and closed malpractice claims. Very few if any ambulatory procedures are emergent, and in comparison to the inpatient population, ambulatory surgical patients are generally healthier. They are still however subject to most of the same types of adverse events as patients undergoing inpatient surgery, albeit at a lower frequency. The only adverse events that could be considered to be unique to ambulatory surgery are those that arise out of the circumstance of discharging a postoperative patient to an environment lacking skilled nursing care. There is limited information on these types of discharge-related adverse events, but the data that are available are reviewed in an attempt to assist the practitioner in patient selection and discharge decision making. Among ambulatory surgical patients, particularly those undergoing screening or cosmetic procedures, expectations from all parties involved are high, and a definition of adverse events can be expanded to include any occurrence that interrupts the rapid throughput of patients or interferes with early discharge and optimal patient satisfaction. This review covers all types of adverse events, but focuses on the more severe adverse events that are associated with morbidity requiring unplanned admission to hospital and mortality.