Surgical Site Infections account for 15-30% of healthcare-associated infections. Surgical antibiotic prophylaxis is one of well-documented measures to decrease the risk of infections. However, many situations threaten its proper application and thereby its effectiveness: patient already receiving antibiotics or carrying resistant germs, clinicians' misunderstanding about timing and duration of antibiotic prophylaxis or patient history of penicillin allergy. In this article we try to clarify these situations to favour good practice in perioperative antibiotic prophylaxis.