BACKGROUND There is increasing evidence that subsyndromal manic symptoms occur frequently during bipolar major depressive episodes (MDEs) and may be a subtle form of 'depressive mixed state.' This paper examines the prevalence and clinical characteristics of MDEs with subsyndromal manic symptoms. The specific effects of overt irritability and psychomotor agitation are examined. METHODS Bipolar (type I or II) patients with an MDE at intake (N=142) were compared based on the presence or absence of concurrent subsyndromal manic symptoms. The groups were further subdivided by the presence of symptoms of overt irritability and/or psychomotor agitation. RESULTS Subsyndromal manic symptoms during bipolar MDEs were highly prevalent (76.1%), and were associated with significantly increased severity of depression/dysphoria in the intake episode, longer episode duration, and more suicidal ideation and behavior (past, current, and during long-term follow-up). Overt irritability and psychomotor agitation were the most prevalent subsyndromal manic symptoms (co-occurring in 57% and 39% of MDEs, respectively), and accounted for most of the negative effects associated with subsyndromal manic symptoms. CONCLUSIONS The findings need to be confirmed in larger samples, which also examine the relationship to adequate antidepressant and/or mood stabilizing treatment. CONCLUSIONS The presence of one or more subsyndromal manic symptoms appears to be the modal presentation of bipolar MDEs and a marker for a subtle form of bipolar mixed depressive state. In particular, patients with symptoms of overt irritability and/or psychomotor agitation should be monitored closely to avoid serious clinical outcomes such as longer affective episodes, exacerbation of manic symptoms syndromal mania, and heightened suicidality.