The paper presents data on the differential fertility of schizophrenics and controls, and the fertility of their siblings. This study used several methodological procedures in the study of schizophrenia reproduction, which strengthens the validity of the findings. Firstly, both male and female rates were examined. Secondly, the method of selection of a control avoided the biases introduced by using census data or other non-matched controls. Third, a diagnostic criterion was used which minimizes the possibility of the inclusion of other psychiatric illnesses. The results obtained support prior reports of the lowered reproductive rates of schizophrenics. Further, the siblings of schizophrenics were found not to have a reproductive advantage when contrasted to control siblings. The failure to find a reproductive advantage conflicts with a hypothesis of a balanced polymorphism as the mechanism maintaining an apparent constant rate of schizophrenia.