Symptoms suggesting gastrointestinal motor dysfunction were determined in 114 diabetic subjects (type 1 and type 2) to see if they were most significantly related to diabetic neuropathy or to psychiatric illness. Presence of neuropathy was established using peripheral nerve conduction studies and objective tests of autonomic function. Affective and anxiety disorders were determined with a structured interview and standard diagnostic criteria. Symptoms were reported by the subsets of subjects with and without neuropathy, ranging in prevalence from 8% to 35%. Log-linear analysis indicated that each group of symptoms (upper gastrointestinal symptoms, altered bowel habits, and abdominal discomforts) was more significantly associated with psychiatric illness (p less than 0.01 for each) than with peripheral neuropathy (p greater than 0.2 for each). In this study, where anxiety and depression were prevalent, no symptom group was significantly associated with autonomic neuropathy once the effects of psychiatric illness on the analysis were taken into account (p greater than 0.2 for each). These findings suggest that gastrointestinal symptoms occurring in diabetic patients are poorly related to neuropathic complications and may often represent gastrointestinal syndromes commonly associated with psychiatric illness.