The aim of the study was to assess the impact of an individual patient order form which concerned the 21 most costly antibiotics in a university hospital. Antibiotics expenditures were monitored from 1995 to 1999 and were expressed in 1999 French Francs per 100 patient days (p.d.). The time series were analyzed by auto-regressive models. The trend of antibiotics expenditures which were concerned by the individual patient order form was a yearly increase of 50 FF/100 p.d. (p < 0.01). The individual patient order form had no significant impact on global antibiotics expenditures but there were some differences across departments: antibiotics costs decreased 1.293 FF/100 p.d. (p = 0.02) in intensive care departments. Monitoring antibiotics consumption should be continued in order to increase power of analysis and to assess the impact of the implementation of guidelines.