Environmental factors effecting the intellectual and emotional development of a person have been fairly well delineated except for the period of fetal intra-uterine life. Certain mental diseases (epilepsy and mental deficiencies) are known to have etiological factors operative in the prenatal and delivery periods. Evidence here reviewed indicates that ill-advised choice of therapy during pregnancy can cause physical defects in the fetus. The likelihood exists that defects of the central nervous system can arise in the same way. If so, the obstetrician shares in the responsibility for preventing mental illness.