The belief that the emotional attitude and behavior of the pregnant woman may affect the child she carries is present in the folklore and ritual of every known human society. Only recently has scientific interest been turned on this subject. The author reviews those observations which substantiate the notion of a prenatal environment and its part in the shaping of the individual's behavior pattern. The mother's negative attitude toward pregnancy may be, by many different means, conveyed to the foetus and reflected in complications of pregnancy or in the child's early deviant behavior. It has been shown that a mother undergoing severe emotional stress tends to have a hyperactive foetus. In turn hyperactive foetuses often tend to become hyperactive infants, irritable, fussy, crying easily, with frequent bowel movements, and food intolerance. In one study the hyperactive foetuses, two and one-half years later were found to be the nursery's problem children.