In high care settings for persons with intellectual disability (ID) aggressive incidents often occur. Still little is known about factors that are associated with an increased risk for aggressive behavior in clients who are admitted to an inpatient treatment facility. In four inpatient facilities, 108 adults with mild and borderline ID and behavior problems were categorised into three aggressive incidents groups (no, mild, severe) according to their actual aggressive behavior observed for six months. The three groups were compared with regard to background and admission characteristics, psychiatric co-morbidity and emotional and behavioral problems. Results show that antisocial behaviors, behaviors indicative of a lack of impulse control, psychotic behaviors, mood related behaviors, and auto-aggressive behavior increased the likelihood of severe aggression. The three groups did not differ with regard to client and admission characteristics or psychiatric co-morbidity. Behaviors that are predictive of severe inpatient aggression in settings for adults with mild to borderline ID and behavior problems closely resemble those that are distinguished in risk assessment instruments for forensic non-disabled individuals. (Contains 4 tables.)