There is a great deal of interest in safety in health care, and the surgical suite is perhaps one of the greatest areas of interest due to the potential for life threatening risk. Nonetheless, the availability of appropriate risk assessment strategies is but in its infancy despite an exponential growth of ambulatory surgery. While there is reason to believe this growth has been conducted in a safe fashion, the increasing acuity of patients and procedures performed in a multiplicity of settings reinforce the need for a scientific determination of risk to aid clinicians and policy makers alike in their work.