The purpose was to examine the long-term stability of a diagnosis of psychotic disorder in adolescence and to focus on diagnostic change over time. A total of 88 patients with a first episode of early onset psychosis (before 19 years) were followed up an average of 10.5 years (range 5.1-18.2) after admission. This report includes the 68 patients who could be traced and interviewed with the Positive and Negative Symptom Scale and lifetime Structured Clinical Interview for DSM-IV diagnosis. An initial diagnostic split between schizophrenia spectrum and affective disorder had a good (> 80 %) Positive Predictive Validity and Sensitivity. The main diagnostic shift was an influx to schizophrenia spectrum disorder (n = 6). These patients resembled the stable affective group (n = 27) in premorbid and prodromal aspects but changed over time to resemble the poor outcome of the stable schizophrenia spectrum group (n = 28) albeit with fewer negative symptoms and a better social function. Family history of nonaffective psychosis in first or second degree relatives was often found in the "change to schizophrenia group". A diagnosis in adolescence of schizophrenia spectrum or affective psychotic disorder is usually stable over time. A subgroup of non-schizophrenia patients go on to develop a schizophrenia spectrum disorder.