ABSTRACTThis article provides practical ethical guidance for clinicians making decisions after a nuclear detonation, in advance of the full establishment of a coordinated response. We argue that the utilitarian maxim of the greatest good for the greatest number, interpreted only as “the most lives saved,” needs refinement. We take the philosophical position that utilitarian efficiency should be tempered by the principle of fairness in making decisions about providing lifesaving interventions and palliation. The most practical way to achieve these goals is to mirror the ethical precepts of routine clinical practice, in which 3 factors govern resource allocation: order of presentation, patient's medical need, and effectiveness of an intervention. Although these basic ethical standards do not change, priority is given in a crisis to those at highest need in whom interventions are expected to be effective. If available resources will not be effective in meeting the need, then it is unfair to expend them and they should be allocated to another patient with high need and greater expectation for survival if treated. As shortage becomes critical, thresholds for intervention become more stringent. Although the focus of providers will be on the victims of the event, the needs of patients already receiving care before the detonation also must be considered. Those not allocated intervention must still be provided as much appropriate comfort, assistance, relief of symptoms, and explanations as possible, given the available resources. Reassessment of patients' clinical status and priority for intervention also should be conducted with regularity.(Disaster Med Public Health Preparedness. 2011;5:S46-S53)