This article concerns a study that examines the attitudes of parents, who have had babies in neonatal care, to sharing their babies' routinely collected health data for research purposes. A participatory methodology was applied to the design of the study; a group of eleven parents who had all previously had babies in neonatal care were involved in designing a large-scale questionnaire survey. The article addresses the rationale for taking this approach, highlighting how it differs from the more common models of patient and public involvement. It presents the five themes that emerged from parents' discussion in the course of engaging in the questionnaire design: legitimation, expertise, experiential knowledge, a different epistemology, power and control. How these shaped the design of the survey is employed in this article as a means of providing a commentary on the participatory research process itself. The article concludes by reflecting on whether participatory research can achieve its aims of promoting social justice when used for instrumental purposes such as the refinement of a data collection tool.