A growing number of researchers have demonstrated an inverse relation between the number of patients treated with specific diagnoses or procedures in a hospital and subsequent adverse outcomes. Such findings support the notion that policies should be explored to concentrate patients in selected hospitals to reduce preventable patient mortality or morbidity. The authors used data from 15 diagnoses and procedures demonstrating an inverse relation between volume and mortality to explore the different implications of regionalization policies across categories of patients. In some instances, concentrating patients in hospitals with high volumes of such patients could avert more than 60% of all deaths. For some procedures or diagnoses, however, such mortality savings are. either medically infeasible because of the emergency nature of the problem or logistically impossible because of the extent of regionalization implied.