The use of antibiotic prophylaxis in surgical patients was evaluated in studies before and after an educational program designed to improve the appropriateness of surgical prophylaxis. The first study included 1,021 patients hospitalized in 27 institutions. The repeat study involved 949 patients hospitalized in 24 of these 27 hospitals. After the educational campaign, there was no change in the proportion of patients who received antibiotic prophylaxis for clean operative procedures. However, the proportion of patients in whom antibiotic prophylaxis was initiated within four hours of skin incision (41% vs 65%, P <.001), the mean duration of antibiotic prophylaxis (2.5 days vs 3.4 days, P <.01), and the proportion of patients who met both of these study criteria (31% vs 53%, P <.001) all had significantly improved. Multihospital educational programs may, at relatively low cost, result in modification of physicians’ antibiotic prescribing.