The incidence of postoperative wound infections is increased up to 35% after gastroduodenal surgery, when gastric motility and acidity are decreased, as in case of gastric ulcer or cancer, obstruction, bleeding, antacid therapy. The endogenous flora contaminating the operative-site consists of organisms of the oropharynx and the jejunum and includes anaerobes like bacteroides, aerobes like streptococci, staphylococci, E. coli. Antimicrobial prophylaxis is therefore indicated in these high risk patients. All groups of antibiotics have been used, however 1st and 2nd generation cephalosporins are the most effective. A single dose given intravenously just before anaesthesia is recommended, a second dose is advisable intraoperatively when surgery is prolonged or massive blood loss occurs. Antibiotic prophylaxis is also recommended in gastric bypass surgery for obesity, but remains controversial for percutaneous endoscopic gastrotomy.