OBJECTIVE: To investigate the connection between overweight and first-episode schizophrenia spectrum as well as non-schizophrenia spectrum psychiatric disorders in adolescent male and female drug-naïve psychiatric inpatients, whose illness was early onset. METHOD: Three hundred twenty-three adolescents with no past or present psychiatric medication, 12-17 years of age, admitted to the psychiatric inpatient care (Oulu University Hospital, Northern Finland) between April 2001 and March 2006. DSM-IV diagnoses were based on the "Schedule for Affective Disorder and Schizophrenia for School-Age Children Present and Lifetime" (K-SADS-PL). An adolescent was defined as overweight if his or her BMI was greater than or equal to the 85th percentile. RESULTS: Overweight values were highest in drug-naïve adolescent boys with first-episode schizophrenia spectrum (RR: 2.5, 95%CI: 1.08-4.29) and non-schizophrenia spectrum (RR: 2.80, 95%CI: 2.20-3.45) disorders. The RR in girls with non-schizophrenia spectrum disorders was 1.73 (95%CI: 1.31-2.23), but in those with first-episode schizophrenia spectrum disorders RR did not differ from general population. CONCLUSIONS: In our study sample of first-episode schizophrenia spectrum drug-naïve adolescents, overweight was shown to be prevalent in all diagnostic groups other than first-episode schizophrenia spectrum psychotic girls. To the best of our knowledge, this is the first study in which overweight was analyzed and verified among drug-naïve adolescent boys, suffering from first-episode schizophrenia spectrum disorder. To what extent our results are applicable to other regions and study groups, remains to be seen.