The reliability of current and lifetime Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV; American Psychiatric Association, 1994) anxiety and mood disorders was examined in 362 outpatients who underwent 2 independent administrations of the Anxiety Disorders Interview Schedule for DSM-IV: Lifetime version (ADIS-IV-L). Good to excellent reliability was obtained for the majority of DSM-IV categories. For many disorders, a common source of unreliability was disagreements on whether constituent symptoms were sufficient in number, severity, or duration to meet DSM-IV diagnostic criteria. These analyses also highlighted potential boundary problems for some disorders (e.g., generalized anxiety disorder and major depressive disorder). Analyses of ADIS-IV-L clinical ratings (0-8 scales) indicated favorable interrater agreement for the dimensional features of DSM-IV anxiety and mood disorders. The findings are discussed in regard to their implications for the classification of emotional disorders.Classification of emotional disorders has been an inexact science, reflected by the modest reliability of many diagnostic categories and marked changes in definitional criteria across editions of the Diagnostic and Statistical Manual of Mental Disorders (DSM; American Psychiatric Association, 1987Association, , 1994. The diagnostic criteria for all anxiety and mood disorders were revised to varying degrees in the current, fourth edition of the DSM (DSM-IV; American Psychiatric Association, 1994). Often, these revisions were guided by reliability findings from large-scale studies of disorders from the revised, third edition of the DSM (DSM-