Small intestinal bacterial overgrowth (SIBO) is characterized by nutrient malabsorption, associated with an excessive number of bacteria in the proximal small intestine. Unfortunately, the diagnosis of bacterial overgrowth presents several difficulties and limitations, and as yet there is not a widespread agreement on the best diagnostic test. SIBO occurs when there are alterations in intestinal anatomy, gastrointestinal motility, or a lack of gastric acid secretion. The true association between SIBO and irritable bowel syndrome and celiac disease remains uncertain. The treatment usually consists in the eradication of bacterial overgrowth with repeated courses of antimicrobials, nutritional support and when it is possible, the correction of underlying predisposing conditions.