BACKGROUND: Overweight is a potential risk factor for peer victimization in late childhood and adolescence. The current study investigated the association between BMI in early primary school and different bullying involvement roles (uninvolved, bully, victim, and bully–victim) as reported by teachers and children themselves. METHODS: In a population-based study in the Netherlands, measured BMI and teacher-reported bullying behavior were available for 4364 children (mean age = 6.2 years). In a subsample of 1327 children, a peer nomination method was used to obtain child reports of bullying. RESULTS: In both teacher- and child-reported data, a higher BMI was associated with more victimization and more bullying perpetration. For instance, a 1-point increase in BMI was associated with a 0.05 increase on the standardized teacher-reported victimization score (95% confidence interval, 0.03 to 0.07; P < .001). Combining the victimization and bullying scores into different types of bullying involvement showed that children with obesity, but not children with overweight, had a significantly higher risk to be a bully–victim (odds ratio = 2.25; 95% confidence interval, 1.62 to 3.14) than normal-weight peers. CONCLUSIONS: At school entry, a high BMI is a risk factor associated with victimization and bullying perpetration, with obese children particularly likely to be victims and aggressors. Results were consistent for teacher and child reports of bullying, supporting the validity of our findings. Possibly, obesity triggers peer problems, but the association may also reflect a common underlying cause that makes obese children vulnerable to bullying involvement.