Long-term institutional care in childhood is linked with behavioral and emotional problems and can negatively affect personality development. This study tested the hypotheses that institutional care constitutes a risk factor for adult personality psychopathology and that conduct disorder acts as a mediator to the institutional care effects, based on 544 community individuals and 470 prisoners aged 18–64 years. Childhood institutional care was associated with elevated dependent, histrionic, and narcissistic traits in the community sample and with schizoid traits in prisoners. Initial findings of associations of institutional care with cluster B personality traits in the two populations disappeared after adjusting for conduct disorder symptoms. Identification and treatment of conduct/behavior problems in children before or during care may help to reduce the risk of developing certain personality disorder traits.