In this study, 64 adults originally (in their childhood) diagnosed with autism were examined for hetero-aggression and its character. Physical hetero-aggression was present in roughly one third of the subjects and, at the same time, it turned out to be dependent on the functional and psychopathological levels of the patients. Occurring only occasionally in high and middle functioning adults as part of a psychopathy-like syndrome, aggression was present in most low functioning patients with catatonic symptoms. These motives for aggressive actions have been revealed: gratifying one's aggressive-sadistic impulses, reaction to one's psychological discomfort, provoking a predictable response. In addition to psychological causes of aggression, the parabulia-related component of autistic adults' aggression is discussed together with the relationship between aggression and dysphoric episodes. Families with an aggressive autistic adult were under significant distress. Quite often the aggression led to injuries of the victims, but the families' need for rehabilitation and psychological counselling wasn't satisfied.