Bipolar disorder (BD) is a chronic psychiatric illness for which there are a number of efficacious and effective treatments. However, for many sufferers recovery is incomplete or tenuous. Factors associated with poor outcomes in the disorder are of special interest, and comorbidity of BD with personality disorder (PD) has been proposed as a possible predictor of poor outcome. We reviewed available studies (n = 12) in the literature that specifically assessed the impact of personality psychopathology on illness outcomes in BD including functioning, response to treatment and suicidality. Quality of methodology, assessment methods and number of participants in studies were highly variable. Despite these variations in study quality, the presence of a PD was robustly associated (usually medium size effects) with a worse outcome in BD. Patients with BD and a diagnosis of PD are more likely to be hospitalized, require more time to achieve symptom stabilization, have more chronic impairments in occupational and social functioning, are less compliant to medication, have greater levels of suicidality and utilize more psychiatric services than patients with BD alone. The implications of these findings for further research and clinical care in BD are discussed. Copyright © 2007 John Wiley & Sons, Ltd.