The etiology of schizophrenia has not been elucidated yet. Since the concordance in monozygotic twins (48%) is higher than in dizygotic twins (17%), a genetic component seems to be involved. Family studies in schizophrenia suggest that this genetic component also plays a part in the etiology of personality disorders, that resemble mild schizophrenia. Moderate concordance between monozygotic twins with respect to the higher concordance between dizygotic twins as compared to siblings who are not pan of a twin, suggest non-genetic factors to be of importance in the etiology of the syndrome as well. Studies on non-genetic risk factors for schizophrehia show the pre- and perinatal period to be clinical in the etiology of the disease. None of these risk factors have been really established to be important in the etiology of schizophrenia.@en