The doctrine of the sinlessness of Jesus has been a given through most of Christian history. After all, if Jesus is God (as in the classic Christological formulations of the early church councils), how could he be a sinner in any sense of the word? The notion of a sinless divine Jesus is directly related to the idea of Jesus as a perfect, sinless human being. Although this doctrine has gone relatively unquestioned for 2,000 years, almost no attention has been given to how this idea developed in early Christianity. Nor have the consequences of this doctrine been sufficiently explored in light of the claim that Jesus is fully human, or as Hebrews 4 puts it, ‘like us in every respect, except sin.’ The goal of this paper is to address both the development of the doctrine of the sinless perfection of Jesus, and to ask if a sinless Jesus is truly human or somehow less than fully human ‘like us.’ My argument is that the sinlessness of Jesus is a case of what might be called ‘retrospective theologizing,’ in which the scandal of Jesus’ death was radically reinterpreted in light of resurrection faith. The retrojection of this faith led to identifying Jesus as a sacrificial lamb who atones for human sin, thus necessitating him to be (like all animal sacrifices) unblemished and, hence, sinless.