This paper describes the prevalence and incidence of psychiatric disorders in IBS patients using a standardized psychiatric interview, and proposes a psychological model for investigating one aspect of IBS. Forty-four IBS patients and 28 nonclinical participants received a psychiatric interview (Diagnostic Interview Schedule) and completed the Lie Scale of the Eysenck Personality Inventory (L-EPI). Results indicated that a significant percentage (59%) of the IBS group met DSM-III criteria for a psychiatric disorder within the last year, far more than occurred in the matched nonclinical comparison group. Relative to the comparison group, the IBS group also had significantly higher lie scores on the EPI indicating a response style of social desirability. On the basis of these findings, together with earlier work by Latimer's group, a conceptual model was formulated on the notion that some IBS patients may have a self-schema (i.e. knowledge of self, stored in memory) characterized by social desirability. We suggest that the construct of self-schema may be helpful in differentiating IBS from psychiatric groups both conceptually and therapeutically.