Antibiotics are prone to misuse. In this study, 37% of 600 antibiotic prescriptions in three hospitals were considered unnecessary. When antibiotic therapy was indicated, 45% were considered to be inadequate. In multivariate analyses, the indicated treatments were found to be more expensive than the unjustified ones, probably because the latter were more often oral regimens. However, for indicated treatments, the cost of adequate and inadequate treatments did not differ significantly.