Background: Small intestinal bacterial overgrowth (SIBO) has been observed in several disorders of the gastrointestinal tract. Studies have shown abnormalities of motor function in obese patients, and there is indirect evidence suggesting that SIBO is present in them. Aims: To study small intestinal motility and the prevalence of SIBO in obese patients and to determine whether there was any relationship between both parameters. Methods: Thirty-nine patients scheduled for bariatric surgery were subjected to hydrogen breath test with lactulose and to a stationary small intestinal motility study with perfused catheters. Results: SIBO was observed in 41% of obese patients and was not related to body mass index. Small intestinal manometry showed a marked increase of clustered contractions in obese patients with SIBO compared to obese subjects without SIBO, whereas all the other parameters of fasting cyclic activity were not different. Conclusions: SIBO was a frequent finding in obese patients and was associated with an increased pattern of clustered contractions, which was not observed in absence of SIBO.