The recent MB case involved a dispute between an infant’s parents and his medical team about the appropriateness of continued life support. The dispute reflected uncertainty about two key factors that inform medical decision making for seriously ill infants: both the amount of pain MB experiences and the extent of his cognitive capacities are uncertain. Uncertainty of this order makes decision making in accordance with the best-interests principle very problematic. This article addresses two of the problems that cases such as that of MB pose for those charged with making medical decisions for infants. First, the question of the moral significance of the interest in avoiding pain is considered. It is claimed that this interest can be outweighed by higher-order interests such as those related to autonomy but that where such higher-order interests do not exist, the interest in avoiding pain should be prioritised. Second, the question of how to proceed in cases in which the level of pain or the extent of an infant’s higher-order interests cannot be decisively established is considered. It is suggested that when genuine uncertainty over the interests of an infant exists, parental views about treatment should prevail.