How should we treat patients diagnosed as being in a persistent vegetative state (PVS) or minimally conscious state (MCS)? More specifically, should we treat them as having the full moral status of persons? Yes, or so we argue. First, we introduce the medical conditions of PVS, MCS, and the related conditions of Locked-in Syndrome and covert awareness. Second, we characterize the main argument for thinking diagnosed PVS patients are not persons. Third, we contend that this argument is defeated by mounting (...) empirical evidence for the considerable uncertainty of PVS diagnoses. Fourth, we characterize a new argument for PVS non-personhood suggested by Neil Levy and Julian Savulescu, one intended to accommodate the diagnostic uncertainty. According to this argument, even if diagnosed PVS patients are in fact MCS, it makes no difference because MCS patients are probably not persons either. Fifth, we challenge the new argument by assembling reasons for doubting the claim that MCS patients are not persons. The outcome is that it is fairly uncertain whether diagnosed PVS and MCS patients are persons or not. What should we do in light of this uncertainty? Sixth, we develop and support a guiding precautionary principle, which we call Precautionary Personhood. Finally, we apply the principle to the case of diagnosed PVS and MCS patients: we argue that given substantial uncertainty about their personhood we should go ahead and treat these patients as if they are persons. (shrink)