Background: A range of benefits have been reported from engaging peer interviewers in qualitative interviews, but little systematic evaluation exists to assess their impact on both process and outcomes of qualitative interviews in health research. Objective: To investigate the impact of involving patient representatives as peer interviewers in a research project on patient empowerment. Design: 18 interviews were carried out as part of the wider study, seven by the academic researcher alone and eleven jointly with a peer interviewer. The interviews were analysed quantitatively and qualitatively to explore potential differences between interviews conducted by the researcher alone and interviews conducted jointly by the researcher and the peer interviewers. A phone evaluation of the peer interviews was carried out with the research participants, and notes were thematically analysed to understand their experiences. Results: Differences were identified between the academic researcher and the peer interviewers in the types of questions they asked and the degree to which personal narrative was used in the interview. Peer interviewers varied significantly in their approach. Research participants were positive about the experience of being interviewed by a peer interviewer. No firm conclusions could be made about impact on outcomes. Discussion and conclusions: The uniqueness and complexity of qualitative interviews made it difficult to provide any firm conclusions about the impact of having peer interviewers on the research outcomes, and the benefits identified from the analysis mostly related to the process of the interviews. Benefits from using peer interviewers need to be considered alongside relevant ethical considerations, and available resources for training and support.