['Centers for Disease Control (CDC) recommend pre-operative smoking cessation to reduce the risk of surgical site infection (SSI). However, whether pre-operative smoking cessation reduces the incidence of SSI for gastrointestinal surgery is unclear. We investigated whether pre-operative smoking cessation reduces the incidence of SSI among patients undergoing gastrointestinal surgery.', 'The study subjects were 512 consecutive patients undergoing gastrointestinal surgery at Osaka Medical Center for Cancer and Cardiovascular Diseases. SSI occurrence was determined by the hospital SSI surveillance team. Pre-operative smoking status was obtained by interview, and the patients were divided into four groups. Information on age, sex, operation time, operational organ, American Society of Anesthesiologists physical status (ASA-PS), elective or emergency surgery, co-existing procedures, use of scopes, ileo-colostomy, properties of drain tube, use of floss, and wound contamination was obtained from the medical records. The relationship between smoking status and incidence of SSI, and risk factors associated with the incidence of SSI were investigated.', 'SSI occurred in 83 patients. Pre-operative smoking status had no relation with the incidence of SSI. Operation time, gallbladder and pancreatic surgery, colon surgery, emergency surgery, co-existing procedures, ilea-colostomy, closed drain, usage of floss, and wound contamination were related significantly with SSI.'] Does [ Pre-operative smoking cessation always reduce the incidence of surgical site infection after gastrointestinal surgery ]?