This article examines the processes of negotiation that occur between patients and medical staff over accessing emergency medical resources. The field extracts are drawn from an ethnographic study of a UK emergency department (ED) in a large, inner city teaching hospital. The article focuses on the triage system for patient prioritisation as the first point of access to the ED. The processes of categorising patients for priority of treatment and care provide staff with the opportunities to maintain control over what defines the ED as a service, as types of work and as particular kinds of patients. Patients and relatives are implicated in this categorical work in the course of interactions with staff as they provide reasons and justifications for their attendance. Their success in legitimising their claim to treatment depends upon self-presentation and identity work that (re)produces individual responsibility as a dominant moral order. The extent to which people attending the ED can successfully perform as legitimate is shown to contribute to their placement into positive or negative staff-constituted patient categories, thus shaping their access to the resources of emergency medicine and their experience of care.