This paper discusses the moral relevance of accounting for various personal characteristics when prioritising between groups of patients. After a review of the results from empirical studies, we discuss the ethical reasons which might explain-and justify-the views expressed in these studies. The paper develops a general framework based upon the causes of ill health and the consequences of treatment. It then turns to the question of the extent to which a personal characteristic-and the eventual underlying ethical justification of its relevance-could have any relationships to these causes and consequences. We attempt to disentangle those characteristics that may reflect a potentially relevant justification from those which violate widely accepted principles of social justice.