A need exists for a self-report questionnaire that reliably and accurately measures symptoms and that distinguishes patients with functional gastrointestinal disease from those with other conditions. We have developed such an instrument, the bowel disease questionnaire, and herein describe details of its discriminatory validity. Data from 399 subjects were analyzed. Patients with gastrointestinal symptoms were ultimately diagnosed as having functional gastrointestinal disease (82 with the irritable bowel syndrome and 33 with functional dyspepsia) or organic gastrointestinal disease (N = 101). There were 145 healthy control subjects and 38 patients with a psychiatric disease, somatoform disorder (which includes those with a diagnosis of hypochrondriasis, psychogenic pain, and somatization or conversion disorder). All subjects completed the questionnaire before undergoing an independent diagnostic assessment by experienced physicians. Functional gastrointestinal disease could be distinguished from organic disease, somatoform disorder, and health by using models derived from logistic discriminant analysis. With use of these models, the estimated probability of functional gastrointestinal disease was then calculated. Descriptive symptom scores were of less value than the scores derived from the data sets by logistic discriminant analysis. Age did not significantly affect the responses to the questionnaire items. We conclude that, in the population studied, the bowel disease questionnaire is a valid measure of symptoms of functional gastrointestinal disease, and this instrument may have clinical and research applications.