This working paper focuses on secondary analysis, an aspect of research practice that is sometimes assumed to pose few ethical challenges. It draws in particular on the experience of a collaborative research project involving secondary analysis of qualitative data collected as part of an ongoing international longitudinal study, Young Lives, and sets this alongside a wider review of regulatory guidance on research ethics and academic debates. Secondary analysis can take many forms, and bring many benefits. But it is more ethically complex than regulatory frameworks may imply.