Summary:The purpose of this article is to review the topic of interictal psychiatric comorbidity among adult patients with chronic epilepsy, focusing specifically on those studies that have used contemporary psychiatric nosology. Five specific issues are addressed: (a) the risk and predominant type(s) of psychiatric comorbidity in chronic epilepsy, (b) adequacy of recognition and treatment of psychiatric comorbidity, (c) the additional burdens that comorbid psychiatric disorders impose upon patients with chronic epilepsy, (d) the etiology of these disorders, and (e) strategies for treatment. Current appreciation for these issues in epilepsy is contrasted to related fields (e.g., primary care, psychiatry, and epidemiology), where considerable attention has been devoted to the identification, consequences, and treatment of psychiatric comorbidity. The issue of psychiatric comorbidity in epilepsy is reviewed with the aim of identifying a clinical and research agenda that will advance understanding of at least one important psychiatric condition associated with epilepsy-namely, major depression. Key Words: Depression-Mood-Epilepsy-Major depressionBehavior-Temporal lobe epilepsy-Complex partial seizures.There is a broad and heterogeneous body of literature relevant to the topic of psychiatric comorbidity in epilepsy. This literature addresses a multitude of behavioral and psychiatric conditions assessed by diverse techniques of variable sophistication, reliability, and validity. These conditions have been examined in varying temporal relationships to the ictus (preictal, interictal, and postictal) in pediatric and adult patients with epilepsy of variable severity and chronicity. Furthermore, several long-standing and seemingly immutable controversies have been an inherent and now burdensome part of this literature.Thus, the first order of business in this review is to sharpen the focus of discussion. This presentation will review interictal psychiatric comorbidity in adult patients with chronic epilepsy and will emphasize investigations using contemporary psychiatric nosology (e.g., Diagnostic and Statistic Manual [DSM] and International Classification of Diseases diagnoses). Five specific issues will be addressed: (a) the risk and predominant types of psychiatric comorbidity in chronic epilepsy, (b) adequacy of recognition and treatment of psychiatric comorbidity, (c) the additional burdens that comorbid psyAddress correspondence and reprint requests to Dr. Bruce P. Hermann at Department of Neurology, University of Wisconsin, 600 N. Highland, Madison, WI 53792. E-mail: hermann@neurology.wisc.eduPresented at the 53rd Annual Meeting of the American Epilepsy Society, Orlando, December 3-9, 1999. chiatric disorders impose on patients with chronic epilepsy, (d) the etiology of these disorders, and (e) strategies for treatment. The current investigation of these issues in epilepsy will be contrasted to that in related fields (e.g., primary care, psychiatry, and epidemiology), where considerable attention has been devoted...