The association between the irritable bowel syndrome (IBS) and psychiatric disorders is well-known to most clinicians, but the nature of the relationship is far from clear. There is an increased prevalence of psychiatric illness in IBS patients and an increase in IBS in psychiatric patients. Whether this association exists outside of treatment-seeking populations (i.e., in IBS sufferers who do not seek treatment) has not been well investigated. This paper will selectively review the existing literature regarding the association of IBS and psychiatric illness in both patient and nonpatient samples. A model of the brain-gut interaction will be presented, as will practical implications of this model for treatment of individuals with IBS.