Background Advance care planning (ACP) in practice often includes conversations with family caregivers of those patientes who have already lost decision-making capacity. This approach has been defined as ACP by proxy and rightly been pointed out as a distict activity, but it blatantly lacks an ethico-legal foundation.

Method Theoretical analysis, drawing from bioethics, philosophical ethics, and international medical law.

Results In contrast to ACP by the patient, ACP by proxy has its core roots not on direct, but indirect patient autonomy. While the patient with his or her autonomous preferences is also at the heart of the process, the epistemological approach to assess these preferences has to pass via surrogates and others close to the patient. As the patient commonly cannot participate in the conversation, his or her preferences cannot be jointly developed by a kind of maieutic process, but have to be approximated by substituted judgment. Another key difference is the ethico-legal responsibility placed on the surrogate decision maker as well as on the health care team and ACP facilitator linked to this substituted judgment.

Conclusion Irrespective of shared values, ACP by the patient and ACP by proxy have distinct ethico-legal features that warrant particular consideration in the practical process of ACP, the qualification of ACP facilitators, and the documents used.