Irritable bowel syndrome (IBS) is a common chronic disease that adversely effects quality of life and is associated with substantial direct and indirect health care costs. It is defined by a constellation of symptoms in conjunction with an alteration in bowel function and defecation, and its underlying pathophysiological basis remains unknown. Numerous therapies are available, but many relieve only one symptom of the syndrome, and their effectiveness has not been demonstrated with adequate evidence from high-quality studies. This article reviews the criteria for appropriate design of any treatment study as well as those criteria specific to studies of treatment for functional gastrointestinal diseases. Using these criteria, the author evaluates the published investigations of "traditional" IBS therapies (antidepressants, bulking agents/fiber, antispasmodics, antidiarrheals) and "alternative" IBS therapies (Chinese herbal supplements, peppermint oil, behavioral therapies). Based on this evaluation, the author concludes that the available evidence does not support the effectiveness of any of these treatments and, therefore, none of these treatments can be reliably recommended.