A new psychiatric report and rating scale assessing severity and frequency of aggressive behaviour is presented and evaluated. It is based on the staff's standardized reports of aggressive incidents. By using a special aggression report form, comprehensive and standardized information is obtained, thereby permitting scoring and further analysis of different aspects of aggressive incidents. The reliability of scoring is tested and found to be good as is the scale's capacity to discriminate between different patterns of aggressive behaviour in different groups of patients. As a result of this and because of the simplicity of the scale, it is thought to be a potentially useful tool in scientific research on aggressive behaviour from psychiatric inpatients.