With the case of Belgium as a negative example, this paper will evaluate the legitimacy of using mentally incompetents as organ sources. The first section examines the underlying moral dilemma that results from the necessity of balancing the principle of respect for persons with the obligation to help people in desperate need. We argue for the rejection of a radical utilitarian approach but also question the appropriateness of a categorical prohibition. Section two aims to strike a fair balance between the competing interests at stake and to define the conditions under which organ harvest from mentally incompetents might be morally acceptable. To this end, we morally assess the main requirements that have been put forward to allow organ removal from incompetent donors. We conclude that the current Belgian legislation is far too permissive and that national regulations that do not permit the harvest of non-regenerable organs from mentally incompetents in exceptional circumstances are too restrictive. On the basis of this discussion, we propose a number of guiding principles for decision-making in this area.