Catechism of the Catholic Church

Organ transplants are in conformity with the moral law if the physical and psychological dangers and risks to the donor are proportionate to the good that is sought for the recipient. Organ donation after death is a noble and meritorous act and is to be encouraged as an expression of generous solidarity. It is not morally acceptable if the donor or his proxy has not given explicit consent. Moreover, it is not morally admissible directly to bring about the disabling mutilation or death of a human being, even in order to delay the death of other persons. (2301)