This article introduces moral distress – the experience of painful feelings due to institutional constraints on personal moral action – as a significant issue for the international health promotion workforce. Our exploratory study of practitioners’ experiences of health promotion in Australia and Canada during 2009–2010 indicated that practitioners who work in upstream policy- and systems-level health promotion are affected by experiences of moral distress. Health promotion practitioners at all levels of the health promotion continuum also described themselves as being engaged in a minority practice within a larger dominant system that does not always value health promotion. We argue that health promotion practitioners are vulnerable to moral distress due to the values-driven and political nature of the practice, the emphasis on systems change and the inherent complexity and diversity of the practice. This vulnerability to moral distress poses significant challenges to both workers and organisations and the communities they seek to benefit. We propose that further research should be undertaken to fully identify the causes and symptoms of moral distress in health promotion. Extensive existing research on moral distress in nursing provides ample resources to conduct such research.