To determine whether bowel symptoms covary in a pattern consistent with the existence of irritable bowel as a distinct syndrome, bowel symptom questionnaires from 2 independent samples were factor analyzed. Samples consisted of 351 18-40-yr-old women who visited Planned Parenthood clinics for contraception and 149 18-89-yr-old women recruited through church women's societies. Factor analysis of 23 bowel symptoms identified 4 factors (clusters of symptoms that were correlated with each other) in both samples. The factor accounting for the most variance in both samples included relief of pain with defecation, looser stools with pain onset, more frequent stools with pain, and gastrointestinal reactions to eating. This irritable bowel factor was not correlated with an objective measure of lactose intolerance. An independent constipation factor was found in both samples to include self-reported constipation, straining with bowel movements, feeling of incomplete evacuation, and rectal bleeding. Thus factor analysis of bowel symptoms supports the existence of a specific irritable bowel syndrome and suggests symptoms that may be used to diagnose this syndrome.