Discussions in neuroethics to date have ignored an ever-increasing neuroscientific lilterature on sex differences in brains. If, indeed, there are significant differences in the brains of men versus women and in the brains of boys versus girls, the ethical and social implications loom very large. I argue that recent neuroscientific findings on sex-based brain differences have significant implications for theories of morality and for our understandings of the neuroscience of moral cognition and behavior.