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 inquire into the ethical reasons which might explain - and justify - the views expressed in these surveys. The paper develops a general framework on the causes of ill health and the consequences of treatment. It goes on to inquire into the extents to which a personal characteristic - and its eventual underlying ethical justification - could have any relationships to these causes and consequences. We attempt to disentangle those characteristics that may reflect a potentially relevant reason from those which violate widely accepted principles of social justice.