Subjects Subjects aged 13-19 were recruited, over 18 months, at mood disorders clinics in 3 tertiary care centres across Canada. Informed consent was obtained from eligible and interested subjects and parents (if subject <16 years of age). Subjects were eligible for entry into the study if they had a diagnosis of Major Depression determined from both clinical interview and the Schedule for Affective Disorders and Schizophrenia for Children (K-SAD-PL) and scored > 16 on the first 17 items of the 29-item Hamilton Rating Scale for Depression (HAM-D). Subjects were excluded if they had past or current hypomanic or manic episode, current psychotic symptoms, substance dependence in the last 3 months, significant medical condition that would contra-indicate the use of antidepressants or that if untreated may require medical attention, pregnancy, or past treatment with sertraline for major depression.