Treatment of bipolar depression with antidepressants is strongly debated for the methodologically poor and insufficient data supporting their use and the widely held belief that antidepressants can induce new episodes of abnormal mood elevation or accelerate the rate of cycling. The present study aimed at identifying clinical risk factors for switch into (hypo)mania or mixed states, within 8 weeks after introduction of an antidepressant or after increasing its dosage, in a prospective, longitudinal design.