Among 1502 aggressive children and adolescents who had been presented and treated at the Department of Child and Adolescent Psychiatry at the University of Tübingen there were 25 who had been cruel to animals. These were exclusively boys (23 out of 25). The age distribution of the zoosadists showed an increased incidence in 13, 17 and 18 year olds which is connected with problems of puberty, group constraints and proving virility. Compared with a control group of "only aggressive" patients, organic brain damage owing to complications of pregnancy or delivery, overtaxing upbringing by the parents and absence of a positive father figure could be demonstrated in the zoosadists. The hypothesis that aggressive children and adolescents have less chance to live out their aggressions in interpersonal relations use zoosadism as "evasion aggression" could only be confirmed in part. One third of the zoosadists showed additional disorders of sexual behaviour and the sexual-sadistic component was manifested in the zoosadistic action.