BACKGROUND AND AIMS Because symptoms alone do not identify pathophysiology or differentiate subgroups of constipation, diagnostic tests are generally recommended. However, their utility is not known. We performed a systematic review of diagnostic tests commonly used in constipation. METHODS We searched the English literature using MEDLINE and PUBMED databases from 1966 to 2004 for studies in adults published as full manuscripts whose methodological quality was above a minimum score. RESULTS No studies assessed the routine use of blood tests or abdominal x-ray. One retrospective endoscopic study showed that cancer and polyp detection rate was comparable to historical controls. Two studies of barium enema were unhelpful in diagnosis of constipation. Physiological studies showed differences in study population, methodology, and interpretation, and there was no gold standard. Ten colonic transit studies showed prevalence of 38-80% in support of slow transit constipation. Nine anorectal manometry studies showed prevalence of 20-75% for detecting dyssynergia. Nine studies of balloon expulsion showed impaired expulsion of 23-67%. Among 10 defecography studies, abnormalities were reported in 25-90% and dyssynergia in 13-37%. CONCLUSIONS Evidence to support the use of blood tests, radiography, or endoscopy in the routine work up of patients with constipation without alarm features is lacking. Colonic transit, anorectal manometry, and balloon expulsion tests reveal physiologic abnormalities in many selected patients with constipation, but no single test adequately defines pathophysiology. Large, well-designed, prospective studies are required to examine the utility of these tests.