Background  Client participation has become a dominant policy goal in many countries including the Netherlands and is a topic much discussed in the literature. The success of client participation is usually measured in terms of the extent to which clients have a say in the participation process. Many articles have concluded that client participation is limited; professionals often still control the participation process and outcomes.Objective  The objective of this study is to gain insight into (i) the practice of client participation within a quality improvement collaborative in mental health care and (ii) the consequences of a Foucauldian conceptualization of power in analysing practices of client participation.Design  We used an ethnographic design consisting of observations of national events and improvement team meetings and interviews with the collaborative’s team members and programme managers.Results  Contrary to many studies on client participation, we found both clients and service providers frequently felt powerless in its practice. Professionals and clients alike struggled with the contributions clients could make to the improvement processes and what functions they should fulfil. Moreover, professionals did not want to exert power upon clients, but ironically just for that reason sometimes struggled with shaping practices of client participation. This mutual powerlessness (partly) disappeared when clients helped to determine and execute specific improvement actions instead of participating in improvement teams.Conclusion  Recognizing that power is inescapable might allow for a more substantive discussion concerning the consequences that power arrangements produce, rather than looking at who is exerting how much power.