Aim: To investigate public health nurses' perceptions and experiences of mental health and of the prevention of mental ill health among women postpartum, within paediatric healthcare services. Background: Although maternal health following childbirth should be a priority within primary care, it is known that women postpartum do not always receive the support they need to adapt to and cope with motherhood. Research implies that postnatal problems lack recognition and are not always acknowledged in routine practice. Few studies have been presented on this topic or from the perspective of nurses. Methods: For this study, eight semi-structured interviews were conducted with public health nurses, and the transcribed texts were analysed through a process inspired by Burnard's description of the four-step qualitative content analysis. Findings: Three categories - external influences on postpartum mental health, screening for and preventing postpartum mental ill health and paediatric healthcare services as a platform for support - were interpreted to reflect the nurses' perceptions and experiences of mental health among women postpartum and of the prevention of mental ill health among women postpartum. Conclusion: We found that public health nurses can have an important role in supporting mothers' mental health postpartum. Although caution is warranted in interpreting our results, the findings concur with those of other studies, highlighting that an equal care emphasis on both the mother and child can be an important aspect of successful support. Implementing person-centred care might be one strategy to create such an emphasis, while also promoting the mental health of new mothers. Public health nurses have a unique opportunity to support mothers' transition into healthy motherhood, especially because they are likely to meet both mothers and children on a regular basis during the first year after birth.