Abstract: Various authors, notably Eaton and Rosen (1980a) and Varian (1980), have proposed that income taxation may be justified to some extent on the ground that it serves as social insurance against uncertainties in labor income. They assume that private insurance is unavailable. primarily because of moral hazard, and demonstrate that some taxation is efficient because the benefits of mitigating risk exceed incentive costs. This note suggests that private insurance should be considered explicitly in examining this question. Moral hazard problems limiting private insurance coverage are not alleviated by government insurance. Moreover, in the presence of moral hazard, government insurance, through labor income taxation or otherwise, may be an inefficient policy because private insurance decisions are distorted. More traditional justifications for redistributive taxation are unaffected by this argument.