OBJECTIVE: Aggressive behaviour is common in young people admitted to child and adolescent inpatient services. Little is known about how physical aggression during admission influences patient outcomes. The aim of the present study was to identify predictors of aggression in a child and adolescent inpatient unit and examine differences in clinical outcomes between aggressive and non-aggressive patients. METHOD: Episodes of aggression occurring within a child and adolescent inpatient unit were prospectively documented between October 2004 and December 2005. Patient factors (demographics, diagnoses, clinical history) were examined as predictors of aggression. Outcomes for admissions in which more than one episode of physical aggression occurred were compared to those in which no aggression occurred. Outcomes assessed were changes in symptom severity (as rated by the Health of the Nation Outcome Scales for Children and Adolescents) length of stay, and initiation of medications. RESULTS: A total of 134 patients were admitted during the study period (61.9% female, mean age=13.8 years, SD=2.9); 31 patients (23.1%) exhibited physical aggression during admission and 20 of these exhibited more than one episode of physical aggression. Factors that predicted persistent physical aggression included history of aggression, use of medications at presentation and absence of self-harm. Persistent aggression was also associated with increased length of stay, but did not compromise improvements in clinical symptom ratings between admission and discharge or lead to increased medication prescribing. CONCLUSION: Contrary to hypotheses and existing research, aggression during admission does not appear to be a barrier to clinical improvement. Further research is necessary to clarify how aggressive children can receive the most benefit from inpatient admission while minimizing the risks to the patient and those around them.