In 2010–2012, I carried out a secondary analysis, using qualitative data, on young adults' experiences of growing up with a chronic illness. I was particularly interested in what it meant to them to control and master their condition, and how their ideas related to their experiences of living with and managing their condition through childhood and/or adolescence. By examining young adults' sense of mastery across a range of medical conditions, the study aimed to provide a better understanding of how and why they manage their condition as they do, and produce recommendations for health service policy and practice for improving the experiences of this group. Here, I describe how I developed the idea for the study and designed it to be carried out through secondary analysis of archived qualitative data. A number of issues are highlighted to help the reader consider how to approach planning and carrying out such a study, as well appraise the quality of such work and be aware of its possible pitfalls. Particular attention is paid to the value of ‘scoping’ archived data to ensure a good fit between the aims of the study and the range of the dataset(s) to be utilised.