Twenty-nine consecutive outpatients with irritable bowel syndrome were given structured psychiatric interviews, as were 33 consecutive medical controls who did not have irritable bowel syndrome. All were from an internal medicine group practice. Seventy-two percent of irritable bowel syndrome subjects had psychiatric illness, with hysteria and depression the most prevalent syndromes. Only 18% of controls had psychiatric illness. The primary physician made an accurate psychiatric assessment in only 28% of the subjects. An awareness of his patient's psychiatric illness is necessary for the physician to provide effective treatment, as for depression, and to spare the patient needless medications, hospitalizations, and surgery, as with hysteria.