Bacterial translocation is the passage of viable endogenous bacteria from the gastrointestinal tract to mesenteric lymph nodes and other internal organs. The aim of this work was to study bacterial translocation in patients operated on for Crohn's disease. Twenty-eight patients, mean age 29 years, not having received any antibiotics since at least 8 days, presenting with ileal (n = 12), ileo-colonic (n = 14) or colonic (n = 2) Crohn's disease were studied. In 25 out of 28 cases (89%) indication for surgery was strictures inducing an upper small bowel distension in 9 out of 25 patients. Mesenteric lymph nodes and liver biopsies, portal blood samples and peritoneum swabs were harvested after laparotomy and before gut opening. Bacterial translocation, defined as the presence of intestinal bacteria in at least one of the specimens, was present in 8 out of 28 patients. This was found in lymph nodes draining surgical territories in 7 out of 8 cases. Bacterial strains involved in translocation included E. coli (n = 5), Enterococcus (n = 3), Clostridium perfringens (n = 2), Proteus (n = 2), and Bacteroides fragilis (n = 1). The rate of translocation differed neither according to Crohn's disease site nor with perforating or non perforating type of the disease. Five out of 9 patients operated on for strictures with proximal distension had a translocation. In conclusion, bacterial translocation was identified in 29% of patients operated on for Crohn's disease in this series. Distension of the intestine proximal to a digestive stricture could favor the occurrence of bacterial translocation in Crohn's disease.