Paranoid schizophrenia is considered to be a rare condition in adolescence. Since this is contrary to the authors' clinical experience, they hypothesized that a controlled study would show that a significant number of adolescents would be diagnosed with paranoid schizophrenia and that scores from the childhood version of the Schedule for Affective Disorders and Schizophrenia (K-SADS) would differentiate between the paranoid schizophrenic adolescents and adolescents with other types of schizophrenia or with affective disorder.The authors conducted a prospective study of 120 adolescents admitted consecutively to an adolescent psychiatric inpatient department. Patients were diagnosed on the basis of DSM-III after an 8-week period during which they were evaluated with a structured psychiatric history and psychiatric examination, the K-SADS, repeated nonstructured interviews, and extensive ward observations.Thirty-eight percent of the schizophrenic adolescents and 14% of the total hospitalized population met the DSM-III criteria for paranoid schizophrenia. The symptom profile of the paranoid schizophrenic adolescents clearly distinguished them from adolescents with other psychiatric disorders.Given the incidence of paranoid schizophrenia in an adolescent population, adolescent psychiatrists are likely to encounter this disorder. DSM-III-R should be used in future studies to further clarify the issue of the prevalence of paranoid schizophrenia in adolescents.