Various patient-, surgery-, an anesthesia-related factors probably influence the outcome of surgical procedures. The American Society of Anesthesiologists (ASA) Physical Status Classification System, while a systematic approach to the assessment of anesthetic risk factors, considers only physical status factors and lacks predictive value for individual cases. Other risk-predictive factors such as age and sex of the patient and the type, site, and duration of surgery should also be included. Multifactorial approaches include both patient- and surgery-related variables, and therefore make an individualized risk prediction possible. Although the choice of anesthetic agent does not appear to influence the incidence of complications or operative outcome, anesthetic technique and anesthesiologist skill are factors of some importance.