Patient engagement is a nebulous term with varied deployment and an unclear definition. This lack of clarity has implications for both understanding the processes involved in engaging patients as well as making sense of patients' uptake of health advice and health outcomes. Furthermore, it remains crucial that a mechanism for measuring and evaluating engagement over time at both local and system wide levels is developed that is most closely aligned and informed by patients' own constructs of engagement. In this paper we present a critical analysis of patient engagement and why it is imperative to develop its conceptual and practical application in primary health care. A patient engagement audit tool (PEAT) for use in primary care is described drawing on a case study approach and the topic of childhood obesity prevention. The case study demonstrates the implementation of the (PEAT), the dynamics of its use, and how it is possible to track progress in patient engagement, or lack thereof, over time. We make tentative conclusions about its potential translation to childhood obesity prevention and other areas.