This study investigated the prevalence of and factors associated with school bullying and victimization among Finnish international adoptees. The Olweus bully/victim questionnaire was sent to all 9–15-year-old children adopted in Finland between 1985 and 2007 through the mediating organizations officially approved by the Ministry of Social Affairs and Health. The children were identified through official adoption organizations. The response rate in the target sample was 49.4%: the study sample consisted of 364 children (190 girls, 52.2%). The children’s background factors and symptoms of reactive attachment disorder (RAD) were evaluated using a FINADO questionnaire. Their learning difficulties and social and language skills were assessed using a standardized parental questionnaire (Five to Fifteen). Of the participants, 19.8% reported victimization by peers while 8% had bullied others. Both victimization and bullying were associated with severe symptoms of RAD at the time of adoption (RR 2.68, 95%CI 1.50–4.77 and RR 2.08, 95%CI 1.17–3.69 for victimization and bullying, respectively). Lack of social skills was associated with victimization (RR 1.74, 95%CI 1.06–2.85) but not independently with being a bully (RR 1.50, 95%CI 0.91–2.45). In a multivariate analysis the child’s learning difficulties and language difficulties were not associated with either bullying others or victimization.