Studies have indicated the importance of family life and psychosocial working conditions for mental wellbeing. More recently, studies have highlighted that a good balance between work and family is crucial for good mental wellbeing. However, few studies compare the relative importance of these factors for mental wellbeing. The main aim of this study was to analyse the relative importance of psychosocial working conditions, family conditions and work/family conflict for mental wellbeing. The analyses are based on a Swedish data set, including questions regarding working life, family life and mental wellbeing. A total of 12,461 married/cohabiting individuals employed in Swedish organisations were included in the study. Results show that psychosocial working conditions, family conditions and work/family conflict all were related to mental wellbeing. In the final regression model, the strongest correlation was found between mental wellbeing and the variables work/family conflict, satisfaction with private life and partner relationship, with work/family conflict appearing to be of greatest importance. These findings highlight the necessity of including measurements of work/family conflict when studying the importance of work and family conditions for individual mental wellbeing. For workplace health promotion and improvement, it may be beneficial to consider not only psychosocial working conditions, but also family conditions, and particularly work/life conflict