To our knowledge, there is no previous clinical description in the literature of patients with defecation syncope. We evaluated 20 patients with this disorder who were a subgroup of a larger, prospective study of syncope, 13 women and seven men, with a mean age of 59 years. Eleven patients had had one episode and nine had experienced multiple episodes. Fourteen patients were recumbent before the urge to defecate, nine of these asleep. The diagnostic evaluation disclosed that two patients had gastrointestinal tract problems, three had cardiac diseases, and one had transient ischemic attacks. Three additional patients had marked orthostatic hypotension. No identifiable cause for defecation syncope was found in 11 patients, but new medical problems were noted in four of those patients. In follow-up at two years, syncope had recurred in ten patients, but the majority of recurrences were unassociated with defecation. Seven patients died during the follow-up period of underlying chronic diseases. We conclude that defecation syncope is not a single distinct clinical entity. Multiple pathologic abnormalities in association with physiologic changes during sleep and defecation may contribute to syncope. Patients with defecation syncope should undergo a careful evaluation for diagnosis of underlying illness causing syncope.