Through using the Experience Sampling Method for nurses working on a High Intensive Care Unit in a large psychiatric hospital in the Netherlands different factors from the staff and the ward were studied to establish their association with the development of aggression within a naturalistic setting. With this study the following factors were found to contribute to the development of inpatient aggression: less availability of the nurse, more working experience, a more negative interaction between the nurse and the patient (such as in setting a limit or discussion about privileges) and an occupancy rate of the beds above 100%. Protective for aggression is a more positive atmosphere on the ward.In knowing this, it is possible to develop more specific strategies to prevent inpatient aggression and more is learned on the nature of violence against staff in mental health (Theme 1).