Summary.Bully/victim problems among six classes of 8–9 year‐old and six classes of 11–12 year‐old children, attending three middle schools, were investigated by means of Olweus's self‐report Bullying Inventory. About 21 per cent of the children reported being bullied, and about 17 per cent reported bullying others, “sometimes” or more often. Reports of both bullying and being bullied were more prevalent among boys than among girls, and among the younger group than among the older group. The two most common forms of bullying were reported to be teasing and hitting/kicking. Fewer of the younger group than the older group reported being bullied by same‐age pupils, and more of the former reported being bullied by older pupils. Most boys were bullied by other boys only, whereas girls were more likely to be bullied by children of either sex. Besides being bullied in school, children also reported that this happened on the journey to/from school and in other places such as in the street near where they live. Many children expressed negative attitudes towards bullying, although nearly a third said that they could understand why it happens. The majority of the children who reported being bullied/bullying others had not been spoken to about this by teachers or by someone at home. Victims of bullying, but not bullies, were found to be most likely to report feeling unhappy and lonely at school, and to report having fewer good friends. In Study 2, children identified as bullies, victims and not involved in this type of problem were interviewed to find out why certain children and/or themselves bully/get bullied by others, and the feelings of the children involved. The pattern of responses by the three groups differed in some