Schizophrenia and bipolar disorder seem to be completely distinct. However, years of intensive investigation on the genetic bases of these disorders suggest that they share common genetic risks.

In order to support this hypothesis, we report the cases of two heterozygous twins. One has been diagnosed with SA and the other with bipolar disorder type II (BPII).

Sirs Z R and T R are 31 years old. They are from a non-consanguineous marriage. Their parents divorced when they were 13 years old. Their mother would be followed for schizophrenia and she is currently stabilized.

Mr. Z R was in school up the third year upper. He is followed in psychiatry for SA since the age of 15 years. He had been hospitalized in the psychiatric department 13 times. The patient is currently well stabilized with risperidone and valproate.

Mr. T R is a teacher of mathematics. He is followed from the age of 18 years for BPII. He presented previously 4 major depressive episodes that would have been of medium intensity and 5 hypomanic episodes.

He was treated with valproate (500mg/day) with a good treatment adherence.

He had been hospitalized once in the psychiatric department for physical and verbal hetero aggressiveness. The final diagnosis over this hospitalization was hypomanic episode with an hysterical personality.

Schizophrenia and bipolar disorder share common genetic risks, therefore early detection of endophenotypes in unaffected relatives of patients with these disorders should allow the development of strategies to prevent them.