During a mass casualty disaster, the acute imbalance between need for treatment and capacity to supply care poses difficult rationing problems. It is common to assume that such disasters call for "utilitarian" procedures that deliberately prioritize saving the most lives over other considerations. A group of medical responders to the 2010 Haitian earthquake faced particular challenges in determining how to allocate limited treatment, time and other resources between existing patients and potential patients not yet under care. We identified that rationing dilemmas points occurred at three points: when care had to be limited, when care had to be completed prematurely, and when care had to be withdrawn. "Repeat triage" refers to rationing challenges occurring at all these points, where the allocation of care is between existing and potential patients. By contrast, "initial triage" designates the allocation of access to treatment among new arrivals, all of whom are potential patients. Repeat and initial triage differ significantly. Several considerations make repeat triage special by supporting limited priority to existing patients, in transgression of pure "utilitarian" procedures: (1) Pragmatically, often it is more efficient to complete treatment on existing patients, for whom prognosis can be established with greater certainty and without added time, than to attempt to save new patients; (2) A fiduciary trust relationship has been formed between care-giver and existing patients, which may make the moral obligation towards them somewhat stronger than the one to potential patients; (3) Existing patients will have often arrived earlier, so when needs are equal, the "first come, first served" principle prioritizes them for care; (4) Withdrawal of care during repeat triage may constitute active rather than passive harm, and more often a serious transgression of patient autonomy; (5) Health providers should normally not be asked to behave in ways that profoundly violate their personal and professional integrity, and abandoning existing patients may do so. For these reasons, responders can permissibly give a degree of priority to existing patients over newcomers in disaster.