Perioperative use of antimicrobial drugs constitutes extra-label use of those drugs. Principles of therapeutic and prophylactic use of antimicrobial drugs can guide decisions about their perioperative use. Regimens currently suggested are based on those principles, theoretical information, pharmacokinetic and pharmacodynamic data, extrapolation from studies with other species, empirical data, personal bias, and experience. Controlled clinical investigations are necessary to provide objective data from which specific recommendations can be derived.