The increase of cesarean sections produced more postoperative infections. Several authors assessed the effectiveness of chemioantibiotic prophylaxis to reduce the postoperative infective morbidity. Although the family of antibiotics more frequently used is that of cephalosporin, the best single agent has not been found yet. The aim of our study, made in the Department of Obstetrics and Gynecology of University of Naples "Federico II", is to propose a retrospective analysis concerning the incidence of cesarean section (CS), the postoperative infective morbidity and the employment of antibiotic prophylaxis. Our sample is a group of 13285 pregnant women, 3171 (23.9%) of these patients underwent to CS from 1st January 1985 to 31st December 1994. The group of 3171 women was divided in two subgroups, the first of 2748 patients un-derwent to antibiotic prophylaxis, the second of 423 was untreated due to their previous experience of allergy towards antibiotics or because there was no evidence of risk factors. The women we treated with antibiotics underwent a three days prophylactic therapy with cefazolin or ampicillin soon after the CS. The incidence of infective complications had a 21.2% rate over a total of 3171 women. Endometritis was the most common infectious complication following cesarean delivery. The rate was 53.3% in the case of primary cesarean section and 52.3% in the case of iterative cesarean section. The use of antibiotic prophylaxis gave us the opportunity to reduce the postoperative morbidity in the primary CS (23.4%) as well in the iterative CS (16.6%). On the contrary the untreated group had an infective incidence with a 33.8% rate in the case of primary CS and with a 27.4% rate in the case of iterative CS. Our opinion is that the administration of antibiotics as cefazolin and ampicillin is able to reduce in a significant way the incidence of postoperative infective morbidity as well the period of hospitalization.