The comorbidity of current and lifetime DSM-IV anxiety and mood disorders was examined in 1,127 outpatients who were assessed with the Anxiety Disorders Interview Schedule for DSM-IV: Lifetime version (ADIS-IV-L). The current and lifetime prevalence of additional Axis I disorders in principal anxiety and mood disorders was found to be 57% and 81%, respectively. The principal diagnostic categories associated with the highest comorbidity rates were mood disorders, posttraumatic stress disorder (PTSD), and generalized anxiety disorder (GAD). A high rate of lifetime comorbidity was found between the anxiety and mood disorders; the lifetime association with mood disorders was particularly strong for PTSD, GAD, obsessive-compulsive disorder, and social phobia. The findings are discussed in regard to their implications for the classification of emotional disorders.