A major use of antimicrobial agents in hospitalized children is prophylaxis of postoperative wound infections. In view of this frequent use and the emerging consensus on recommendations for prevention of surgical wound infections,1 the American Academy of Pediatrics has developed guidelines for surgical antimicrobial prophylaxis in children. Prophylaxis is defined as use of antimicrobial drugs in the absence of suspected or documented infection. FREQUENCY OF ANTIMICROBIAL PROPHYLAXIS In an extensive study of patients in acute care general hospitals in Pennsylvania, 36% of antimicrobial courses were initiated for prophylaxis of infection after surgery or an invasive procedure, such as cystoscopy or cardiac catheterization.2 The prevalence and reasons for antimicrobial use have been studied primarily in general or adult hospitals, but the patterns of use in children are similar to those in adults.3-5 Two studies have demonstrated that prophylaxis accounts for approximately 75% of the antibiotic use on pediatric surgical services.4,6 The efficacy of antimicrobial prophylaxis in lowering the incidence of postoperative infection after certain types of surgery has been demonstrated amply in controlled clinical trials.7 These and earlier studies by Miles et al8 and Burke9 in experimental animals have delineated the principles for effective use of antimicrobial agents in surgical prophylaxis, including choice of drugs and when and how long they are to be given. INAPPROPRIATE ANTIMICROBIAL PROPHYLAXIS Prophylaxis has been incriminated as a major cause of inappropriate use of these antimicrobial agents in both adults and children.4,5,10-12 In 74% of antimicrobial courses given for prophylaxis in the Pennsylvania study, the duration exceeded 48 hours, an interval beyond which continuation has not been proven beneficial.2