['Prophylactic administration of antibiotics can decrease postoperative morbidity, shorten hospitalization, and reduce overall costs. In Western countries, it is stressed that antimicrobial prophylaxis was discontinued within 24 hrs after surgery in currently published guidelines. However, it is unclear how long we need to continue perioperative prophylaxis for gastrointestinal surgery. In this manuscript, we analyzed surgical site infection (SSI) in gastric and colorectal surgery according to the duration of antibiotics prophylaxis and discuss the duration of an antibiotic prophylaxis, and its relation to SSI.', 'We studied 228 patients who underwent digestive surgery including 94 with gastric cancer, 85 with colon cancer and 49 with rectal cancer.', 'Overall SSI was seen in 28 cases (12.2%), 8 cases (8.5%) in gastrectomy, 10 cases (11.8%) in colectomy and 10 cases (20.4%) in rectal surgery. In SSI positive cases, operative time was longer (p=0.01), blood loss was more (p=0.01) and duration was longer (p=0.01) than in SSI negative cases. The duration of prophylactic antibiotics was significantly longer in 28 patients with SSI than in the 200 non-SSI patients (3.5 +/- 1.8 vs. 2.3 +/- 1.7 days; p<0.05).'] Does prolonged antibiotic prophylaxis longer than 24 hours decrease surgical site infection after elective gastric and colorectal surgery?