This research explored the extent to which Child and Family Health Nurses (CHNs) exercise autonomy as specialist health professionals within community health settings. Using postnatal depression (PND) as an example we examined if, and how, CHNs exercised autonomy within their practice, drawing on their specialised body of knowledge. A qualitative study was undertaken using in-depth interviews with 10 CHNs practising in Tasmania, Australia. We analysed the interview data thematically to identify how CHNs defined and discussed PND, the strategies they drew on in their practice, and indicators of professional identity and autonomy in their descriptions of practice as it pertained to PND. Three themes emerged from this analysis: alternative understandings of maternal sadness; technicality, indeterminancy and tacit knowledge; and identification of professional boundaries. We found that CHNs' autonomous practice was informed by understandings distinct from dominant perspectives, suggesting that this specialist area of nursing practice exhibits extensive indicators of professionalism that have been largely unrecognised. This has implications for both CHNs' professional identity and the provision of services available to new mothers and their babies.