This analysis was conducted on baseline data from 178 nonadherent bipolar disorder subjects in a randomized controlled trial. Medication adherence was measured with Tablets Routine Questionnaire as percentage of days with missed doses. Inclusion criteria required at least 20% nonadherence. Medication adherence, symptomatology, and functioning in individuals with and without a comorbid anxiety disorder were compared. There were 78.9% of subjects who had at least one or more current anxiety disorder, with the most common being posttraumatic stress disorder, panic disorder, and generalized anxiety disorder. The percentage of days with missed doses over the past month was significantly lower in those with anxiety disorders compared with those without (40.1% vs 50.5%, p = 0.03). Those with comorbid anxiety disorders and those with greater number of anxiety disorder diagnoses had significantly worse mean scores on the Montgomery-Åsberg Depression Rating Scale, Brief Psychiatric Rating Scale, Clinical Global Impression–Bipolar Version, and Global Assessment of Functioning.