Bipolar patients are much more likely to present to clinicians, especially in outpatient settings, when they are depressed (Hirschfeld et al., 2005). However, unipolar depression is more prevalent than bipolar disorder: the lifetime prevalence of unipolar major depressive disorder is 16.2%, whereas the lifetime prevalence of bipolar spectrum disorders is 4.5% (Table 1) (Kessler et al., 2003; Merikangas et al., 2007). The clinical presentation of a patient with bipolar disorder when depressed may not differ from that of a non-bipolar depressed patient. In light of the higher prevalence of unipolar depression compared with bipolar disorder and the similarities in clinical presentation of a depressive episode in both unipolar and bipolar depression, without appropriate screening, bipolar patients may be misdiagnosed.