Background: Individuals with bipolar disorder (BD) often possess maladaptive traits and present with various difficulties in psychosocial functioning. However, little is known about the intimate partners of adults with bipolar disorder (BD) and how mental illnesses other than BD within couples may further complicate the picture. Such knowledge is needed to inform both couple and family interventions.

Methods: Participants were parents whose children were enrolled in a prospective study: 55 with BD and their partners, and 47 healthy control couples. All completed diagnostic interviews, and questionnaires describing personality traits, negative life events, coping skills, social support, marital adjustment and inter-partner verbal aggression. Parents with BD and healthy control parents were compared, as were the intimate partners. A series of exploratory analyses focused on the average measures within couples, with and without BD, and took account of comorbid personality disorders among those with BD and major depressive disorder among their partners.

Results: Intimate partners of adults with BD, relative to healthy control partners, presented with more mental disorders, higher neuroticism, lower extraversion, more emotion-focused coping, smaller social networks, less satisfaction with their social networks, and little, satisfying social contact. Additionally, they reported less consensus and satisfaction in their marital relationships, and engaged in more verbal aggression towards their partners. Participants with BD showed similar, more extreme, characteristics. Marital distress and verbal aggression were greatest among couples with an adult having BD and a comorbid personality disorder or a partner with major depressive disorder.

Conclusion: This study contributes to the literature by demonstrating that both parents with BD and their intimate partners exhibit high levels of mental illness, maladaptive personality traits and psychosocial difficulties, thus limiting their partners' ability to provide support and stability in the these high risk families. Moreover, mental illnesses other than BD may contribute to marital problems within couples. Some statistical analyses, particularly those involving comorbid conditions, were under-powered in this study. As clinical implications, the current study suggests that both individuals with BD and their partners could benefit from interventions aimed at lowering emotionality and verbal aggression, and increasing social support and effective coping skills.