To examine the predictors of aggressive behaviours occurring before acute hospitalisation.

We analysed 350 acute admissions to a psychiatric ward during a 12-month period. The diagnoses were formulated according to the DSM IV axis I and II criteria. Aggressive behaviours occurring in the week before admission were retrospectively assessed using the modified overt aggression scale. The patients' clinical and sociodemographic variables, concurrent drug or alcohol abuse, and admission status were recorded at the time of admission.

Aggressive and violent behaviours were highly prevalent, respectively, in 45% and 33% of the cases. Violence before admission was independently associated with drug abuse, involuntary admission status, and severe psychopathology. A diagnosis of a psychotic disorder did not increase the risk of aggression or violence, compared to the other psychiatric diagnoses. Personality disorders were significantly more associated to aggressive behaviours than psychotic disorders.

The diagnosis of psychotic disorder is a poor predictor of aggression in a sample of psychiatric patients. Other clinical and non-clinical variables are associated to aggression before hospitalisation: they include drug abuse, involuntary admission status, general severity of symptoms, and diagnosis of personality disorder.