Pre-natal infection with polioviruses could contribute to the subsequent development of schizophrenia. The hypothesis draws support from the declining incidence of schizophrenia, the excess of schizophrenic winter births, and the increased rates of schizophrenia among West Indian immigrants. There are parallels with other late sequelae of poliovirus infections. These postulations generate a testable hypothesis of a genetic link between schizophrenia and susceptibility to poliomyelitis.