In the context of lay mobilization in health-related areas, this article addresses the role and activities of patients' associations in connection with organ donation, on the basis of interviews carried out with thirty members of transplant patients' associations in the French-speaking part of Switzerland. First, we describe the three main categories of activities conducted by these associations. While self-help and public awareness activities are predominant, policy-oriented actions are marginal. Then, we examine the factors likely to explain why these associations have a limited capacity to be active, especially in the public sphere. Such a lack of social visibility is all the more important in the current political context, characterized by the implementation of a national action plan designed to improve organ donation.