A sound evaluation of every bioethical problem should be predicated on a careful analysis of at least two basic elements: (i) reliable scientific information and (ii) the ethical principles and values at stake. A thorough evaluation of both elements also calls for a careful examination of statements by authoritative institutions. Unfortunately, in the case of medically complex living donors neither element gives clear-cut answers to the ethical problems raised. Likewise, institutionary documents frequently offer only general criteria, which are not very helpful when making practical choices. This paper first introduces a brief overview of scientific information, ethical values, and institutionary documents; the notions of “acceptable risk” and “minimal risk” are then briefly examined, with reference to the problem of medically complex living donors. The so-called precautionary principle and the value of solidarity are then discussed as offering a possible approach to the ethical problem of medically complex living donors.