The purpose of this study was to determine the patterns of gastrointestinal and anal sphincter motility in 25 consecutive patients with severe constipation. Three patterns of abnormal motility were observed in 68% of the patients: (a) isolated anal sphincter dysfunction (20%), (b) a generalized disorder of gastrointestinal motility (24%), and (c) rectosigmoid dysfunction (24%). The remaining patients had either a previously unrecognized primary disorder leading to constipation or the irritable bowel syndrome. Duration of symptoms, laxative usage, or other historical features failed to distinguish each of the groups. Anal sphincter dysfunction was diagnosed by demonstrating impaired sphincter relaxation during rectal distention. Generalized motor disorders were diagnosed by demonstrating impaired colonic and esophageal function together with an abnormality in gastric emptying. Rectosigmoid dysfunction was manifest by an impaired rectosigmoid motor response to feeding without evidence of other organ dysfunction. These studies indicate that a high percentage of patients with more severe degrees of constipation have a serious but sometimes treatable disorder of bowel function, rather than the irritable bowel syndrome.