Adolescent-onset psychoses often raise diagnostic difficulties because of the mixture of schizophrenic and affective features. This study examined prospectively which clinical dimensions contribute to difficulty in initial diagnosis and which clinical features have predictive value for outcomes of schizophrenia or affective disorders, and for eventual psychosocial functioning. Thirty-six adolescents consecutively admitted for a psychotic episode were followed up for 1 to 4 years. Symptoms were assessed at admission, at discharge, and once a year. DSM-III-R (APA 1989) diagnoses were assessed at admission and once a year. Comparisons were performed across initial and followup diagnostic groups. Positive symptoms did not differentiate the initial clinical pictures, while negative symptoms, manic symptoms, and disorganization differentiated the manic and depressive episodes in the acute phase. When initial positive symptoms (mainly delusions) were severe, they predicted a final diagnosis in the schizophrenia spectrum. Poor outcome was associated with more anhedonia-associality and lower functioning scores at admission. Results suggest (1) a higher vulnerability to positive symptoms in adolescents who will further develop schizophrenia and (2) the low specificity of affective symptoms at this age.