By means of projective identification, parents may contribute to the differential life course leading to schizophrenia in a family member. The author presents the case history of a family with a set of monozygotic male twins discordant for schizophrenia. The father, by suggesting that one twin was more vulnerable than the other, helped establish in that twin a negative identity, an inhibition (rather than a neutralization) of instinctual expression, and an aggressive (rather than libidinal) tie with the parents. The ego splitting that resulted seemed to be based on the child's projective identification in a pathologically defensive way.Abstract Teaser