Bipolar affective disorder (BPD) frequently occurs with co-morbid mental health problems. This study shows that that the prevalence of co-morbid BPD and anxiety symptoms is especially high. This is important because for a person affected by both BPD and anxiety there is a negative impact on the symptoms, treatment response and recovery. A clinician faces particular treatment challenges when managing these co-morbid conditions due to a limited evidence base for effective interventions. The frequent occurrence of anxiety symptoms and BPD together has informed theories of the shared aetiology of these conditions.