Access to public healthcare services for Belgium’s undocumented migrants is regulated through a parallel, administrative procedure within the legal framework of Urgent Medical Aid. This imposes several constraints on their access to healthcare services. Drawing on empirical-ethical methodologies, we show how this procedure impacts on the relationship between patients with undocumented status and healthcare workers. We use the concept of relational autonomy to show how the imposed legal constraints reduce the formal treatment options available to healthcare workers, but simultaneously lead (...) to informal care practices, and how the latter increase the discretionary power of the healthcare workers. We argue that in this context, provision becomes unpredictable and arbitrary, with undocumented migrants tending to value strong personal relations with one particular, trusted healthcare worker. Although this leads to increased dependence, it also increases patients’ options and autonomy by providing access to wider professional networks attached to that healthcare worker. (shrink)