The authors evaluated existing and new criteria for defining the medical necessity for breast reduction surgery. Two cohorts of women (those requesting breast reduction surgery [N = 266] and a group of controls [N = 184]) completed a questionnaire including breast-specific symptom severity, the Short Form 36, the EuroQol, the McGill Pain Questionnaire, and the Multidimensional Body Self Relations Questionnaire. To evaluate prediction validity, the most widely accepted decision criteria and a new definition of medical necessity were applied to the data set to determine whether women meeting the definition had more favorable outcomes than those who did not as measured by validated self-report instruments. For existing criteria, women not meeting and meeting the criterion gained equal benefit from surgery. Women meeting the new definition (2 of 7 physical symptoms all or most of the time) had significantly greater improvement scores on 4 of the 5 health burden measures compared to women not meeting this definition. The authors conclude that medical necessity for breast reduction surgery is better defined by self-report of symptoms than by existing criteria.