Studies on small intestinal transit in irritable bowel syndrome (IBS) are scarce and inconclusive. The contribution of intestinal dysmotility to the development of small bowel bacterial overgrowth (SIBO) in these patients remains to be elucidated. The aims of this study were to assess the orocecal transit time (OCTT) and the frequency of SIBO in IBS patients, the relationship between these two parameters, and their respective associations with clinical features, body mass index (BMI) and psychological distress. Methods. Ninety consecutive IBS patients were studied. All of them answered a structured questionnaire for demographic and clinical data. The presence of anxiety and depression was assessed by the Hospital Anxiety and Depression scale. Hydrogen breath test after lactulose ingestion (LHBT) and glucose hydrogen breath test (GHBT) were used for the assessment of OCTT and SIBO respectively. IBS group were compared to age-matched healthy volunteers, recruited among the hospital staff (n = 25, OCTT and n = 20, GHBT). Results. OCTT in IBS patients (77 ± 36 min) was significantly higher than in controls (64 ± 40 min; p = 0.03). Individual analysis showed prolonged OCTT (> 80 min) in 28.9% of IBS patients, and SIBO in 15.5%. The only symptom significantly associated with SIBO was diarrhea (p = 0.03). In addition there was a significant relationship (p = 0.005) between SIBO and prolonged OCTT. OCTT was not associated (p > 0.05) with intestinal complaints, BMI, anxiety or depression. Conclusions. About one third of IBS patients present prolonged OCTT, indicating delayed small bowel transit. This abnormality appears to be a predisposing condition for the development of SIBO. SIBO is more frequent in IBS patients with diarrhea. © 2016, Sociedad Argentina de Gastroenterologia. All Rights Reserved.464314321