Although aggression is part of daily life in psychiatric units for adolescents, empirical data on its prevalence are sparse. Only few studies have described prevalence of aggressive incidents in adolescent psychiatric wards, and data in forensic psychiatric care are even more limited. Available studies reported high prevalence rates of aggression, ranging from 0.4 to 2.4 incidents of aggression per day across (forensic) child and adolescent psychiatric units. Between 27 and 78 % of all admitted youth committed an aggressive act. In this study, we collected systematically registered data of all aggressive incidents from the first 2 years (2010–2012) on a newly established forensic adolescent psychiatric unit, which used a formal aggression management program embedded in the social competence model, which is based on early intervention in the ‘chain of behavior’ to prevent any further escalation. The inclusion of also minor aggressive incidents is unique in the literature and the clinical relevance is highlighted. A mean of one incident a day took place, with each adolescent involved in at least one incident. Notably, 1.7 aggressive incidents per month made seclusion of restraint use necessary. Based on the social competence theory, the aggression management model suggests intervening early in the cascade of aggression, in order to prevent further escalation and reduce the need for intrusive interventions. Evidence supported that aggression is a contextual event, as external factors clearly influence the incidence of aggression. Aggression management should be built on both relational and structural security.