Measuring the frequency of a defined outcome flaw for a series of patients undergoing operative procedures generates information for performance evaluation. Such data influence decisions to improve care if used responsibly. Wound infection (WI), bacterial invasion of the incision, is the most common infectious complication of surgical care and WI prevention has value because the complication affects economic, patient satisfaction, and patient functional status outcomes. WI frequency, one kind of surgical outcome flaw rate, is traditionally used to judge one aspect of surgical care quality. At the author's institution, global WI surveillance was conducted without interruption for 20 years. Results for 85,260 consecutive inpatient operations performed during the period showed that secular changes in infection rates occurred but were not necessarily caused by surgical care quality decrements.