Postoperative infections are the most frequent cause of morbidity and mortality in surgical patients, considerably increasing the duration and cost of hospitalization. During the past decade the criteria for the administration of prophylactic antibiotics have been established and their proper use has caused a significant reduction of postoperative infections. The Authors review the indications to the use of local and systemic antibiotic prophylaxis; moreover, the general principles of antibiotic prophylaxis are presented and discussed, including problems related to the choice of antibiotic, dosage, timing and duration of administration, under different clinical circumstances and in various types of surgical operations.