The objective of this prospective study was to test the hypothesis that 6 reportedly important psychosocial factors were useful criteria for diagnosing the irritable bowel syndrome. Ninety-seven new patients with entry complaints of abdominal pain, altered bowel habits, or both underwent full evaluation by board-certified or -eligible gastroenterologists in an outpatient setting. The independent measures were 6 questionnaires concerning anxiety, depression, stress, lack of social support, somatization, and abnormal illness behavior. The dependent measure, irritable bowel syndrome, was defined as the absence of an organic disease explanation for patients' entry complaints. Two other board-certified gastroenterologists, independent of the study, made this determination. Their rating was based on full review of transcripts of patients' clinic visits, laboratory data, and the results of a 9-mo telephone follow-up to patients and their physicians. Sixty-five percent of the sample had no organic disease explanation for the entry symptoms, thereby representing irritable bowel syndrome. The psychosocial predictors did not show a significant association with irritable bowel syndrome; the power of the study was 0.86. Post hoc analysis revealed that patients with organic disease, as well as patients with irritable bowel syndrome, had significantly more (p less than 0.01) psychosocial abnormality than normal subjects, which likely contributed to the inability of the psychosocial predictors to distinguish irritable bowel syndrome from organic disease. It was concluded that psychosocial criteria were of limited value in differentiating irritable bowel syndrome from organic disease but that they were determinants of health care seeking for the entire study group.