Aims: To investigate whether weight category (underweig-ht, average weight, overweight, and obese) at age 7.5 predicts bullying involvement at 8.5 years. Models were tested separately for boys and girls to investigate gender differences in association patterns. Methods: Prospective cohort study in southwest England. Height and weight were measured in children at age 7.5 (n = 8210). BMI (kg/m2) was used to define underweight, average weight, overweight, and obese children, according to British age and gender specific growth reference data. Overt (n = 7083) and relational (n = 6932) bullying behaviour was assessed in children at age 8.5. Results: After adjustment for parental social class, compared to average weight boys, obese boys were 1.66 (95% Cl 1.04 to 2.66) times more likely to be overt bullies and 1.54 (1.12 to 2.13) times more likely to be overt victims. Obese girls were 1.53(1.09 to 2.15) times more likely to be overt victims compared to average weight girls. Conclusions: Obesity is predictive of bullying involvement for both boys and girls. Preadolescent obese boys and girls are more likely to be victims of bullying because they deviate from appearance ideals. Other obese boys are likely to be bullies, presumably because of their physical dominance in the peer group. Aims: To investigate whether weight category (underweig-ht, average weight, overweight, and obese) at age 7.5 predicts bullying involvement at 8.5 years. Models were tested separately for boys and girls to investigate gender differences in association patterns. Methods: Prospective cohort study in southwest England. Height and weight were measured in children at age 7.5 (n = 8210). BMI (kg / m2) was used to define underweight, average weight, overweight, and obese children, according to British age and gender specific growth Overt (n = 7083) and relational (n = 6932) bullying behavior was assessed in children at age 8.5. Results: After adjustment for parental social class, compared to average weight boys, obese boys were 1.66 (95% Cl 1.04 to 2.66) times more likely to be overt bullies and 1.54 (1.12 to 2.13) times more likely to be overt Victims. Obese girls were 1.53 (1.09 to 2.15) times more likely to be overt victims compared to average weight girls. ty is predictive of bullying involvement for both boys and girls. Preadolescent obese boys and girls are more likely to be victims of bullying because they deviate from appearance ideals. Other obese boys are likely to be bullies, presumably because of their physical dominance in the peer group.