The primary goal of the proposed trial is to assess the short- and long-term efficacy of cognitive behavior therapy (CBT) for irritable bowel syndrome using two treatment delivery systems (self administered, therapist administered). Secondary aims seek to specify the conditions under which CBT may (or may not) achieve its effects (moderator questions), why and how these effects are achieved (mediator questions) and at what economic cost. Long term project goals are to develop an effective self-administered behavioral treatment program that can enhance the quality of patient care, improve clinical outcomes, and decrease the economic and personal costs of one of the most prevalent and intractable GI disorders.