Two hundred and three male remanded prisoners were interviewed with respect to their current offence, mental state, and social and psychiatric histories. All but nine of the sub-group of 121 psychotic men showed active symptoms at the time of committing a criminal offence; 20% of the actively ill psychotics were directly driven to offend by their psychotic symptoms, and a further 26% probably so. If some of the indirect consequences of the psychosis were taken into account, 82% of their offences were probably attributable to the illness. Among the normal and neurotic men, none claimed psychotic motives for offending, but motives suggesting high emotional arousal such as panic or retaliation triggered the greatest violence. Within the psychotic group, those driven to offend by their delusions were most likely to have been seriously violent, and psychotic symptoms probably accounted directly for most of the very violent behaviour.