There is a broadly held view that neonatologists are ethically obligated to act to override parental nontreatment decisions for imperiled premature newborns when there is a reasonable chance of a good outcome. It is argued here that three types of uncertainty undercut any such general obligation: (1) the vagueness of the boundary at which an infant’s deficits become so intolerable that death could be reasonably preferred; (2) the uncertainty about whether aggressive treatment will result in the survival of a reasonably (...) healthy child or, alternatively, the survival of a child with intolerable deficits; and (3) the inability to determine an acceptable ratio between the likelihoods of those two outcomes. It is argued that the broadly held view accords insufficient weight to the fact that newborn intensive care increases the likelihood of harm to the child by effecting survival with intolerable deficits. Though treatment may offer a reasonable chance of a good outcome, it is argued that there are situations in which neonatologists should nonetheless defer to parental nontreatment decisions. (shrink)