The costs of antibiotics in Belgian hospitals are nearly fully reimbursed by the health insurance. Such a situation is not conductive to rational drug use. A new reimbursement system for perioperatively-administered antibiotics in Belgian hospitals was implemented in May 1997 by Royal Decree. A reimbursement code for antibiotic use was linked to the reimbursement of surgical interventions. This code represents a reimbursement which covers 75% of the cost of perioperative prophylaxis based on optimal indication, dose, and duration as recommended by international and Belgian consensus guidelines. The actual antibiotic prescribed during the 72-hour perioperative period (the day before, during and after surgery) is reimbursed at only 25% of its full cost. Thus, if the perioperative prophylactic antibiotic regimen complies with the evidence-based guidelines, the costs of antibiotic prescribing will be fully reimbursed by the health insurance (75% of the standard +25% of the actual costs). The new reimbursement system does not apply to antibiotics which are prescribed for treatment of intercurrent infections; these antibiotics continue to be fully reimbursed. Annual expenditures for antibiotics, for both antibiotic treatment and prophylaxis, nationwide and per hospital, have shown marked improvements in perioperative antibiotic use after the decree was implemented. Surgeons' adherence to the evidence-based standard of prophylactic antibiotic use has improved over time. In conclusion, rapid implementation of the perioperative antibiotic prophylaxis policy was achieved through changes in the reimbursement of antibiotics for surgery patients.