OBJECTIVES. A number of studies have shown that victimization from bullying behavior is associated with substantial adverse effects on physical and psychological health, but it is unclear which comes first, the victimization or the health-related symptoms. In our present study, we investigated whether victimization precedes psychosomatic and psychosocial symptoms or whether these symptoms precede victimization. DESIGN. Six-month cohort study with baseline measurements taken in the fall of 1999 and follow-up measurements in the spring of 2000. SETTING. Eighteen elementary schools in the Netherlands. PARTICIPANTS. The study included 1118 children aged 9 to 11 years, who participated by filling out a questionnaire on both occasions of data collection. OUTCOME MEASURES. A self-administered questionnaire measured victimization from bullying, as well as a wide variety of psychosocial and psychosomatic symptoms, including depression, anxiety, bedwetting, headaches, sleeping problems, abdominal pain, poor appetite, and feelings of tension or tiredness. RESULTS. Victims of bullying had significantly higher chances of developing new psychosomatic and psychosocial problems compared with children who were not bullied. In contrast, some psychosocial, but not physical, health symptoms preceded bullying victimization. Children with depressive symptoms had a significantly higher chance of being newly victimized, as did children with anxiety. CONCLUSIONS. Many psychosomatic and psychosocial health problems follow an episode of bullying victimization. These findings stress the importance for doctors and health practitioners to establish whether bullying plays a contributing role in the etiology of such symptoms. Furthermore, our results indicate that children with depressive symptoms and anxiety are at increased risk of being victimized. Because victimization could have an adverse effect on children's attempts to cope with depression or anxiety, it is important to consider teaching these children skills that could make them less vulnerable to bullying behavior. Copyright © 2006 by the American Academy of Pediatrics.