Corticosteroids are used in the management of intestinal obstruction (IO) in carcinomatosis peritonei. There is considerable overlap in the symptoms experienced in IO and functional adrenal insufficiency (AI). The success of symptom palliation in IO may be related to the presence of AI. The aim of this preliminary study was to evaluate the incidence of functional adrenal insufficiency in patients with IO and its relation to clinical outcome and symptom control. Twenty-nine consecutive patients with IO and carcinomatosis peritonei from gastrointestinal cancers admitted to our inpatient service between January and October 2002 were analyzed. They were screened for AI using the short corticotropin stimulation test. Thirteen patients (45%) had functional AI. Differences in characteristics of patients with normal adrenal function (Group 1) and adrenal insufficiency (Group 2) were not statistically significant. Time taken to control symptoms in Group 2 was longer. Mean duration of hospitalization per month of survival was two times longer in Group 2 relative to Group 1 (7.9 versus 4.0 days, P=0.011). Functional AI may be caused by cytokines produced in advanced cancer mediating direct adrenal suppression. Prompt corticosteroid therapy in the presence of AI may facilitate IO symptom palliation.