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To be efficient, an action on psychosocial risks requires a questioning of the organization, the distribution of power and decision processes. The aim of this paper is to discuss theoretical and methodological stakes of an ergonomic intervention on psychosocial risks. First, a theoretical frame is proposed, to support the legitimacy of an ergonomic intervention on psychosocial risks. Suffering expressed by the operators is linked to production difficulties stemming from organizational malfunctioning, notably difficulties faced by the workers when trying to « work well ». An example of an intervention in a service company is presented. The concept of subsidiarity is proposed as a guide for the ergonomists’ thinking on organizational design.