I. The order of birth of the retardate or mentally defective child is apparently of little significance.II. The foreign-born mothers (43 per cent of the population of the towns surveyed) are over-represented as mothers of our group. They make up 68 per cent of the mothers of retarded children and 75 per cent of the mothers of mentally defective children.III. Families having a mentally defective child [I.Q. -.70; mean = 6.24 ± .03 (S. D.)] show a tendency to be larger than families having a retarded child [I.Q. +.70; mean= 5.71 ± .04 (S. D.)]. These figures include all families, both complete and incomplete.IV. Native-born mothers of retardates and mental defectives in our group have larger families than native mothers of the same age groups in New York State. This condition applies also to foreign-born mothers of retardates and mental defectives of the age groups-20, 20-24, and 25-29 years. Foreign-born mothers of the age groups 30 years and over show a tendency to have smaller families than foreign mothers of the same age in the general population.V. The mean number of children ever born in completed families is recorded as follows by mental condition of child and nativity of mother:Native-born mothers of retardates (I. Q., .70+) = 6.52 ± .21(S. D.).Native-born mothers of mental defectives (I. Q., -.70)= 6.84 ± .23(S. D.).Foreign-born mothers of retardates (I. Q., .70+) = 7.54 ± . 11(S. D.).Foreign-born mothers of mental defectives (I. Q., -.70)= 7.64 ± .09(S. D.).VI. In this sample, completed families with a child in the lower levels of intelligence are approximately twice as large as completed families with a child in the upper levels of intelligence. The stocks represented in this sample which are producing retarded or mentally defective children are more than maintaining themselves.