It has been suggested that agitated depression (AD) is a common, severe feature in bipolar disorder. We aimed to estimate the prevalence of AD and investigate whether presence of AD was associated with episodic and lifetime clinical features in a large well-characterised bipolar disorder sample. The prevalence of agitation, based on semi-structured interview and medical case-notes, in the most severe depressive episode was estimated in 2925 individuals with DSM-IV bipolar disorder recruited into the UK Bipolar Disorder Research Network. Predictors of agitation were ascertained using symptoms within the same episode and lifetime clinical features using multivariate models. 32.3% (n=946) experienced agitation during the worst depressive episode. Within the same episode, significant predictors of presence of agitation were: insomnia (OR 2.119, p<.001), poor concentration (OR 1.966, p=.027), decreased libido (OR 1.960, p<.001), suicidal ideation (OR 1.861, p<.001), slowed activity (OR 1.504, p=.001), and poor appetite (OR 1.297, p=.029). Over the lifetime illness course, co-morbid panic disorder (OR 2.000, p<.001), suicide attempt (OR 1.399, p=.007), and dysphoric mania (OR 1.354, p=.017) were significantly associated with AD. Agitation accompanied bipolar depression in at least one-third of cases in our sample and was associated with concurrent somatic depressive symptoms, which are also common features of mixed manic states. Furthermore, AD in our sample was associated with lifetime experience of mixed mania, in addition to severe lifetime illness course including comorbid panic disorder and suicidal behaviour. Our results have implications for the diagnosis and treatment of agitated features in bipolar depression. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.