Our aim was to study the presence of personality traits and disorder in adolescents with Chronic Fatigue Syndrome (CFS). Personality was then compared to other measures of functioning such as presence of psychiatric disorder and rating on the Child Behavior Checklist 4-18 (CBCL) and in relation to CFS outcome. Twenty-five adolescents with CFS followed-up after contacts with tertiary paediatric/psychiatric clinics were compared with 15 matched healthy controls. Interviews and questionnaires from parents and youngsters included Personality Assessment Schedule (PAS), Kiddie-SADS Psychiatric Interview, Child Behavior Checklist. CFS subjects were significantly more likely than controls to have personality difficulty or disorder. Personality features significantly more common amongst them were conscientiousness, vulnerability, worthlessness and emotional lability. There was a nonsignificant association between personality disorder and worse CFS outcome. Personality difficulty or disorder was significantly associated with psychological symptoms and decreased social competence on the CBCL but it was distinguishable from episodic psychiatric disorder. Personality difficulty and disorder are increased in adolescents with a history of CFS. Personality disorder may be linked to poor CFS outcome.