Seclusion with or without restraint is a measure for managing aggressive or agitated clients and promoting site security, particularly in an emergency psychiatric setting. The decision to control a potentially dangerous person's behaviour by removal or seclusion seems ethically justifiable in such a setting. However, although the decisions on these restrictive measures are based on rational needs, they are also influenced by the healthcare team's perceptions of the client and by the characteristics of the team and the environment. The purpose of this paper is to set out and categorize the factors in play in aggression- and agitation-management situations as perceived by the healthcare teams, particularly the nurses. The first part of the paper deals briefly with the settings in which control measures are applied in a province in eastern Canada and the effect of such measures on patients and healthcare teams. The second part identifies the factors involved in the management of agitation and aggression behaviour. The final part discusses the current spin-offs from this knowledge as well as promising paths for further research on the factors involved. The ultimate objective is to reduce recourse to coercive measures and enhance professional practices.