The participants will be in-patients experiencing psychotic aggression (determined by psychiatrist). For those patients experiencing aggression (which is not severe enough to require intramuscular injection), the treating clinician will make a decision whether or not to treat with Quetiapine XR. Those patients meeting inclusion/exclusion criteria will be observed over 8 days using measures that rate symptoms, aggression and possible side effects (these include observation, questionnaire and review of patient files).