Health promotion interventions can be improved using methods from behavioural economics to identify and target specific decision-making biases at the individual level. In this context, prospect theory provides a suitable framework within which decision-making processes can be operationalised. Focusing on a trade-off between health outcomes and behaviour change incurred by chronic disease management (lifestyle change, or ‘self-management’), we are the first to measure the risk attitudes and quantify the full utility function under prospect theory of a patient population. We conducted a series of hypothetical elicitations over health outcomes associated with different self-management behaviours from a population of individuals with or without ‘manageable’ chronic disease (n?=?120). We observed risk aversion in both the gain and the loss domains, as well as significant loss aversion. There seems to be an age effect on risk attitudes in this context, with younger people being on average less risk averse than older people. Our work addresses a need to better understand these decision-making processes, so that behaviour change interventions tailored to specific patient populations can be improved.