Purpose – The aim of the research is to assess the extent and value of mental health service user (MHSU) involvement in research in England. Design/methodology/approach – This is a knowledge review, including academic and “grey” literature, and documented testimonial evidence. Findings – The involvement of MHSUs in mental health research has become mainstream. There is clear evidence that involving MHSUs in research adds value. Four gaps in the literature were identified. First, a lack of evidence from non-service-user researchers about their experience of working with MHSUs. Second, a lack of recognition that anyone involved in research may hold more than one role. Third, failure to treat carers as separate from MHSUs, or – often – to include them at all. Fourth, a lack of understanding that MHSUs may have a useful role to play in research on topics other than mental health. Research limitations/implications – The literature would benefit from some evidence about non-service-user researchers’ experiences of working with MHSU researchers. Carers should be recognised much more widely as different from MHSUs and with a valid role to play in mental health research from their own perspectives. MHSU researchers, and carer researchers, should be offered opportunities for involvement in research on topics other than mental health. Practical implications – The evidence shows that involving service users in research can benefit everyone involved and the research itself. The process can be challenging for all concerned. However, there is now plenty of guidance about how to involve service users in research for maximum benefit to all (e.g. Faulkner, 2004b; SURGE, 2005; Morgan, 2006; Tew et al., 2006; Kotecha et al., 2007; Schrank and Wallcraft, 2008, pp. 243-247; Leiba, 2010, pp. 160-169; Armes et al., 2011; Morrow et al., 2012, p. 114). This guidance should be consulted by researchers, funders, ethics committees, and other stakeholders at the earliest possible stage of any relevant project. Social implications – It is essential to recognise and acknowledge that anyone involved in research may hold more than one role. Embracing multiple and mutable identities is not an easy process, as the literature shows, and attempts to do so are likely to produce resistance at every level. Nevertheless, the example of the survivor researchers suggests that doing this has the potential to enrich our individual and collective experience, and therefore society as a whole. Originality/value – The paper is written by an independent researcher who is also a carer for people with mental health problems: a viewpoint which is rarely found in the literature. The literature suggests that power imbalances and identity issues are at the root of most difficulties and gaps. Social identity and categorisation theory offers a useful theoretical perspective. The paper will be of value to anyone interested in mental health research, whether as a student, service user/survivor, researcher or teacher.