Mood disorders in general, and bipolar disorder in particular, are unique among the psychiatric conditions in that they are associated with extraordinarily high rates of comorbidity with a multitude of psychiatric and medical conditions. Among all the potential cormobidities, co-occurring anxiety disorders stand out due to their very high prevalence. Outcome in bipolar illness is worse in the presence of a comorbid anxiety disorder. The coexistence of an anxiety disorder presents a particularly difficult challenge in the treatment of bipolar illness since antidepressants, the mainstay of pharmacologic treatments for anxiety, may adversely alter the course of manic-depression. Identification of anxiety disorders in bipolar patients is important. The treatment plan needs to balance the potential benefit and harm of antidepressant administration.