With the expansion of ambulatory surgery in the Western world over the last 10 years, it has become increasingly important to identify patients at risk of perioperative complications and to use appropriate methods to decrease these risks. The confidential enquiry into perioperative deaths was one of the first national programmes instituted to identify patients at risk after the operation. Although the focus for this initial enquiry was on perioperative mortality, recent developments have increasingly focused on identification of perioperative morbid events. The first large prospective study on outpatients found a very low incidence of death after ambulatory surgery, but with the acceptance of high-risk patients for ambulatory surgery in recent years it is likely that perioperative morbidity will increase in the future. Therefore, identification of the patient at risk is important in order to apply known strategies to decrease these risks. We first need to know what tools are available to detect these 'at-risk' patients. Unfortunately, many of the tools used are very subjective and lack both sensitivity and specificity. In this chapter, an attempt has been made to outline the risks related to surgery, anaesthesia, the patient and the procedure, and finally the role of the establishment. Later, strategies are discussed which could reduce the perioperative general and cardiorespiratory risks in the ambulatory surgical patient. Many of these strategies are derived from the inpatient since appropriate data in outpatients are lacking. Future studies should thus focus on data derived from outpatients and prospective, randomized, double-blind studies in a large population of patients in order to first identify the patient at risk and subsequently to use drugs and techniques that reduce these perioperative risks.