To investigate the factor structure of psychotic symptoms, we compared the clinical characteristics of manic patients with those of schizophrenic patients evaluated with positive and negative syndrome scale (PANSS). The clinical symptoms of 148 bipolar patients and 86 schizophrenic patients hospitalized for an index psychotic episode were assessed. Schizophrenic patients showed more positive and cognitive symptoms than bipolars. The factor analysis of the two PANSS scores showed a three-factor solution with 'positive', 'negative' and 'mixed' depressive-activated factors for bipolars and 'positive', 'negative' and 'depressive' factors for schizophrenics. In both groups, the 'cognitive cluster' loaded on the first 'positive' factor while the 'lack of insight' (LOI) has a different meaning in the two groups, more related to the positive symptoms in the bipolar patients and more related to the negative symptoms in the schizophrenic patients. This finding suggests that LOI could be a non-unitary phenomenon in psychoses and it should be further explored to better elucidate differences in symptom structures between schizophrenic and bipolar disorders.