Am J Psychiatry (subscription) - USA
OBJECTIVE: The authors provide a detailed perspective on the correlates of comorbid anxiety in a large, well-characterized sample of bipolar disorder patients. ...
http://ajp.psychiatryonline.org/cgi/content/abstract/161/12/2222

Felt it important to highlight the conlusions:

CONCLUSIONS: An independent association of comorbid anxiety with greater severity and impairment in bipolar disorder patients was demonstrated, highlighting the need for greater clinical attention to anxiety in this population, particularly for enhanced clinical monitoring of suicidality. In addition, it is important to determine whether effective treatment of anxiety symptoms can lessen bipolar disorder severity, improve response to treatment of manic or depressive symptoms, or reduce suicidality.