Seclusion of patients on psychiatric wards is a controversial intervention with serious safety issues for patients. Nurses have an important role in the decision to use seclusion when encountering aggressive behaviour. The aim of this thesis is to improve knowledge about the influence of nurses on the incidence of aggressive behaviour and the use of seclusion, in order to use that knowledge to prevent such events in the future. Patients and nurses share views on the factual cause of aggressive behaviour, but their perception of the severity differ. The attitude of nurses towards seclusion changed over the last decades from a therapeutic paradigm to a safety paradigm. In our study, teams with majority of male nurses were associated with less seclusion and aggressive behaviour. Teams with high scores on personality trait openness were associated with less seclusion and teams with high scores on personality trait extraversion were associated with patients’ aggression. There are no golden solutions to improve safety of psychiatric wards, but increased attention of development of nursing skills seems as an important step forward. By providing optimal nursing care, vulnerable patients on psychiatric wards receive the care they deserve.