High rates of anxiety disorders have been reported in bipolar disorders. We undertook this study to determine the impact of anxiety disorders on bipolar disorders in our tertiary care referral center. We reviewed the literature on this topic and also reviewed records of 44 treatment resistant bipolar patients evaluated by DLD at the Center for Anxiety and Depression. Twenty-three patients had comorbid panic disorder, posttraumatic stress disorder, or obsessive-compulsive disorder. We compared bipolar patients with and without a history of comorbid anxiety disorders regarding several clinical factors, including mean age, percentage of women, mean age of onset, history of suicide attempts, history of rapid cycling, history of substance abuse, family history, and mean ratings for mood rating scales. Statistical differences were assessed by chi(2) and t-tests. On several measures, bipolar patients with comorbid anxiety disorders were more significantly ill than bipolar patients without comorbid anxiety disorders. For instance, patients with an anxiety disorder were more likely to have an earlier age of onset of illness, have higher (worse) ratings on the Hamilton Anxiety Rating Scale, 17-item Hamilton Depression Rating Scale, Montgomery and Asberg Depression Rating Scale, Beck Depression Inventory, and lower (more impaired) ratings on the Global Assessment of Functioning Scale. Comorbid anxiety disorders were also associated with a more frequent history of substance abuse and higher ratings for suicidal ideation. Anxiety disorders negatively impact the course of bipolar disorders. The high prevalence and risk rate of comorbid anxiety disorders in bipolar patients highlight the need for greater clinical attention to this population.