BackgroundAntipsychotic drug use among children and adolescents is increasing, and there is growing concern about off-label use and adverse effects. The present study aims to investigate the incidence, psychiatric co-morbidity and pharmacological treatment of severe mental disorder in Norwegian children and adolescents. MethodsWe obtained data on mental disorders from the Norwegian Patient Registry on 0–18 year olds who during 2009–2011 were diagnosed for the first time with schizophrenia-like disorder (International Classification of Diseases, 10th revision codes F20-F29), bipolar disorder (F30-F31), or severe depressive episode with psychotic symptoms (F32.3 or F33.3). Data on filled prescriptions for psychotropic drugs were obtained from the Norwegian Prescription Database. ResultsA total of 884 children and adolescents (25.1 per 100 000 person years) were first time diagnosed with schizophrenia-like disorder (12.6 per 100 000 person years), bipolar disorder (9.2 per 100 000 person years), or severe depressive episode with psychotic symptoms (3.3 per 100 000 person years) during 2009–2011. The most common co-morbid mental disorders were depressive (38.1%) and anxiety disorders (31.2%). Antipsychotic drugs were prescribed to 62.4% of the patients, 72.0% of the schizophrenia-like disorder patients, 51.7% of the bipolar disorder patients, and 55.4% of the patients with psychotic depression. The most commonly prescribed drugs were quetiapine (29.5%), aripiprazole (19.6%), olanzapine (17.3%), and risperidone (16.6%). ConclusionsWhen a severe mental disorder was diagnosed in children and adolescents, the patient was usually also prescribed antipsychotic medication. Clinicians must be aware of the high prevalence of depressive and anxiety disorders among early psychosis patients.