In recent years, shortages of radioisotopes that cannot be stockpiled have created a scenario in which they may be considered, periodically, a scarce medical resource. This discussion focuses on the just allocation of medical radioisotopes and presents the dominant ethical frameworks for rationing and priority setting in the patient populations most affected. Priority setting is necessary when demand for a scarce resource exceeds supply. On completion of this article, the reader will be able to describe the origins of rationing and priority setting in medicine, as well as ethically sound frameworks for rationing. Finally, the process for priority setting and the need for transparency of this process in the nuclear medicine setting are outlined.