There is a lack of knowledge about the incidence of personality disorders and their consequences among peacekeepers. Moreover, most studies are follow-up studies in which, if at all, personality traits are screened for after the soldiers have left their service abroad. The aim of this paper was to study personality disorders in a longitudinal perspective. The method used was to screen the personnel in a Swedish mechanized battalion serving in Bosnia from March until October 1996 on four occasions: before deployment, immediately after deployment, 6 months after deployment and 1 year after deployment. Serving in the battalion were 724 individuals of whom 516 took part in the survey. The screening instrument used was the DSM-IV and ICD-10 Personality Questionnaire (DIP-Q). The result shows that the rate of personality disorders were on the same level, or a little bit lower, than in the general population. Moreover, personality disorders were related to impaired general mental health and to reported traumatic experiences. Personality disorders also seemed to contribute to poor mental health 1 year after returning home from a mission abroad. The implications of these results for the future selection of peacekeepers are discussed.