The efficiency of prophylactic antibiotics in total hip replacement has been demonstrated by several studies. The rate of infection decrease approximately from 3 % to 1 % with a cephalosporine 1 protocol. The rate of infection was not different after a five-day administration of cephalosporine 1 and a 2-day treatment of cephalosporine 2. In open fractures, the value of prophylactic antibiotics has to take in account the usual organisms of peroperative contamination as well as the anaerobes. Short administration can be used, however no randomized studies have proven their efficiency. For clean, planned surgery (grade II in the classification of Health National Research Council), prophylactic antibiotics seem to be of value. However, the prescription should not be systematic, but correlated with the local conditions of surgery and the infection rate of the type of the planned procedure.