To explore the difference in the clinical features between bipolar disorder and unipolar depression from the clinical phenomenology.

Two hundred bipolar patients with their current depressive episode and five hundred and sixty three recurrent depression were involved in the study. Clinical features of these two groups were compared and stepwise Logistic regression was used to identify the relationship between clinical features and bipolar disorder.

Clinical features of depressive episode which was different between two groups and were associated with bipolar disorder were as follows: age at onset of bipolar was earlier than that of unipolar depression; Bipolar patients whose age at onset before 25 years were more than unipolar depression; Sexual appetites which was one of atypical depressive symptoms were more common in bipolar depression than in unipolar depression; with psychiatric symptoms, psychomotor retardation, mood instability and duration of every depressive episode < 3 months, were more common in bipolar depression group than in unipolar depression group; Cognitive impairment factor, one of factors of HAMD-17 score, was significantly higher in bipolar depression group than in unipolar depression group. The odd ratio were 1.54, 1.50, 3.25, 1.99, 1.89, 1.48, 1.63, 1.63, and 1.42 separately.

The founding suggested that unipolar depression and bipolar depression might be distinct disorder, and age at onset, age at onset < 25, sexual appetites, psychiatric symptoms, psychomotor retardation, mood instability and duration of every depressive episode < 3 months might be potential to be the predictors of bipolar disorder.