Accurate diagnosis of bipolar disorder is essential for effective treatment. The diagnosis of bipolar disorder is particularly complex, resulting in lengthy delays between first presentation and initiation of appropriate therapy. Inappropriate therapy destabilises the course and outcome of the disease. Although the defining features of bipolar disorder are manic or hypomanic episodes, patients typically present for treatment of depression and commonly deny symptoms of mood elevation. A correct diagnosis can easily be masked by comorbidities, personality issues and complex phenomenology. A diagnosis of bipolar disorder can be assisted by: asking about symptoms of mania or hypomania in every patient presenting with symptoms of depression. recognising mixed states in which manic and depressive symptoms occur simultaneously. identifying the features of bipolar depression that distinguish it from unipolar depression. There is a risk of over-diagnosis of bipolar disorder among patients who are histrionic, show abnormal illness behaviour and/or have issues of secondary gain.