“Mobbing”, i.e. school children repeatedly ganging up on the same victims, was studied among 434 12–16 years old children in three schools in Finland. A group of bullies and a group of victims were selected on basis of peer ratings. 13.7% of the boys and 5.4% of the girls were involved in mobbing behaviour. The children's personality variables were studied with questionnaires. The victims had low self-esteem, were subjectively maladjusted, and experienced their peer relations negatively. The victims were physically weaker than well-adjusted children, and obesity and handicaps were more common among them. The bullies were physically strong, and handicaps were also among them more frequent than among well-adjusted children. The bullies held positive attitudes towards aggression, experienced their peer relations negatively, and held negative attitudes towards teachers and peers. They were unpopular among their peers, though not so unpopular as the victims.