This paper develops a challenge to theism. The challenge is to explain why the hypothesis that there exists an omnipotent, omniscient and all-good god should be considered significantly more reasonable than the hypothesis that there exists an omnipotent, omniscient and all-evil god. Theists typically dismiss the evil-god hypothesis out of hand because of the problem of good–there is surely too much good in the world for it to be the creation of such a being. But then why doesn't the problem (...) of evil provide equally good grounds for dismissing belief in a good god? I develop this evil-god challenge in detail, anticipate several replies, and correct errors made in earlier discussions of the problem of good. (shrink)