Background Recent studies have suggested that functional classifications of aggression should be used to improve the understanding of the heterogeneity of aggression and its management, among inpatients in psychiatric hospitals. Aims Our aim was to examine a theoretically derived three‐factor model for conceptualising aggressive incidents by inpatients as irritable, instrumental or defensive. Methods As part of the routine assessments in a forensic psychiatric high security ward, staff filled out a questionnaire on motives for aggression after all violent incidents. A total of 1652 incidents from 28 patients were analysed by means of exploratory and confirmatory factor analyses. Results Support was found for the three‐factor model. For the most part, the scale items loaded on the factors as predicted, and the model was able to explain 61% of the data variance. Irritable incidents were the most common, but elevated scores for instrumental characteristics were found as well. High psychopathy scores were associated with incidents scoring high values on both irritable and instrumental dimensions, and low values on the defensive dimensions. Conclusions Confirming these three dimensions of inpatient aggressive incidents may help caregivers' understanding of aggressive behaviour. If confirmed in future studies, this dimensional approach may prove useful for the management of aggressive inpatients. Copyright © 2013 John Wiley & Sons, Ltd.