Data on the relationship between small intestinal motility, absorption, and nutrition are sparse and incomplete. Yet, impaired motility is considered to be a plausible cause of bacterial overgrowth, which may have deleterious effects on digestion and absorption. This review discusses the scientific validity and clinical relevance of the concept that intestinal motor abnormalities are responsible for enteric bacterial overgrowth. Disorders associated with intestinal dysmotility and bacterial overgrowth, are illuminated, and concurrent studies of intestinal motility and microflora are focused on in detail. Moreover, practical considerations are given with regard to the clinical management of patients with bacterial overgrowth. Available data allow the conclusion to be drawn that impaired intestinal motility, as evidenced by attenuated migrating motor complex activity, results in bacterial overgrowth. The criteria for an intestinal motility disorder likely to result in bacterial overgrowth have been determined in patients with late radiation enteropathy, but studies in other clinical conditions are needed to establish general guidelines.