Individuals afflicted with childhood and adolescent mental disorders have an increased risk for poor outcome in adulthood. The progression of psychopathology from childhood to adult life may be influenced by a multitude of interacting variables, both biological and psychosocial. There is limited information on the relationships between child psychopathology and adult personality and personality disorders. The main aim of this thesis was therefore to gain better knowledge concerning adult personality outcome in patients with early onset of mental disorders. Former child psychiatric patients as compared to controls had a significantly higher prevalence of all DSM-IV personality disorders (38.0 vs. 10.9 percent, p<0.001) and also a considerably higher personality disorder co-morbidity. They also had more psychosocial and environmental problems. This was exaggerated in those diagnosed with a personality disorder. Major depression, disruptive disorders and substance use disorders at a young age were strong predictors for adult personality disorder. Patients with an early onset major depression had more personality disorders and more deviant personality traits than those with a late onset. Forensic psychiatric male patients diagnosed with a previous conduct disorder as compared to those without had more cluster B personality disorders, and more repeated violent criminality and mixed abuse. They also exhibited more deviant personality traits and higher psychopathy scores. The instrument "Child and Adolescent Psychiatric Screening Inventory-Retrospect" had acceptable sensitivity and specificity for assessment of child psychiatric disorders. Subscales demonstrated good internal reliability (Crohnbach´s alpha = 0.76-0.93). The results suggest that adult personality disturbances are prevalent in individuals affected with mental problems at young ages. A better understanding of the transition of psychopathology from childhood to adulthood and a better identification of those at risk will be of help in attempts to prevent permanent impact on the adult personality