Small bowel bacterial overgrowth is a syndrome manifested by malabsorption, weight loss, and diarrhea. Human intestinal flora is part of a complex ecosystem regulated by host mechanisms, environmental factors, and bacterial interactions. Numerous conditions can tilt this balance to favor bacterial contamination of the gut. Knowledge of intestinal microbial control enables the clinician to better understand the pathophysiology and the clinical features of this disorder. Current strategies in diagnosis and therapy are discussed.