In the first part of this paper, we defend the distinction between treatment and enhancement and argue that a commitment to theism (Christian theism in particular) is a good reason for treating this distinction as a morally relevant one. If human nature is the design of a wise and loving Creator, then it is plausible to maintain that acceptance of our limitations is not merely morally right, but is in fact good for us. Reshaping our own nature by means of technological enhancements or genetic engineering, on the other hand, is plausibly understood as both wrong and bad. We argue that this claim should be understood in terms of species norms and does not apply in individual cases. But what if one does not accept a Christian picture of human nature? Are there secular reasons for believing that this distinction marks a morally relevant difference between two kinds of medical practices? In the second part of the paper, we address these sorts of questions. We argue that there are indeed considerations available to the non-theist which suggest that enhancement, though not obviously morally wrong, is more morally difficult to justify than mere treatment. These considerations include the possibility of harm to those who receive enhancements, the autonomy of future persons, and problems of distributive justice.