When an abortion is performed, someone dies. Are we killing a human person? Widespread disagreement exists. However, it is not necessary to establish personhood in order to establish the wrongness of abortion: a substantial chance of personhood is enough. We defend The Do Not Risk Homicide Argument: abortions are wrong after 10 weeks gestation because they substantially and unjustifiably risk homicide, the unjust killing of a human person. Why 10 weeks? Because the cumulative evidence establishes a substantial chance (a more (...) than one in five chance) that preborn human beings are persons after 10 weeks (if not before then). We submit evidence from our bad track record, widespread disagreement about personhood (after 10 weeks gestation), problems with theories of personhood, the similarity between preborn human beings and premature newborns, miscalculations of gestational age, and the common intuitive responses of women to their pregnancies and miscarriages. Our argument is cogent because it bypasses the stalemate over preborn personhood and rests on common ground rather than contentious metaphysics. It also strongly suggests that society must do more to protect preborn human beings. We briefly discuss its practical implications for fetal pain relief, social policy, and abortion law. (shrink)