The coexistence of anxiety and depression is common and frequently poses diagnostic and treatment challenges in the clinical setting. Although precise diagnosis is important for treatment selection, it is often complicated by the shortcomings of the current classification system. Whereas some patients present with symptoms that meet the diagnostic criteria for both an anxiety disorder and major depression, others may present with "subsyndromal" symptoms of depression and/or anxiety. Epidemiologic data and a rational treatment approach to the patient with mixed anxiety and depression, depressive symptoms coexistent with "syndromal" and "subsyndromal" symptoms of generalized anxiety disorder, panic disorder, obsessive compulsive disorder, and social phobia are discussed, as well as areas of future research to examine coexisting anxiety and depression.