The poor outcomes of young people with chronic health conditions indicate that current services and self-care programmes are not meeting the needs of young people. How young people self-manage their condition impacts on long-term health outcomes, but there is little published evidence that details the development of self-care programmes and their most effective components. This article reports on an innovative formative research study, the purpose of which was to develop a self-care intervention prototype. Participants were 87 young people, aged 12-17, and seven young adult facilitators, aged 18-25, with type 1 diabetes or asthma. Each contributed to talking groups exploring themes that young people wanted to be addressed within a self-care programme. Instead of being focused on "illness", young people's main concerns were directed toward "life as an adolescent", while at the same time building sustainable daily routines of self-care. Overall, this article illustrates the process of initiating and implementing a developmental approach focused on young people, while also demonstrating the tailored self-care intervention that the process developed. This approach can be used to involve young people in the design and development of other conditions that rely on self-care interventions.