Ovaries of children with Down's syndrome were examined histologically in order to determine in what way the ovarian development differed from the normal. Twenty-six specimens obtained at autopsy at various ages between birth and 14 1/2 years were available and compared with ovaries from normal children of similar ages. All ovaries from normal children were characterized by active follicle growth. The ovaries of the children with Down's syndrome, however, showed absence or retardation of follicle growth. Furthermore the number as well as the size of the antral follicles differed from those in the normal ovary. The decrease of the number of small follicles occurs earlier in life in the ovaries of children with Down's syndrome than in the control. The possible relationship between an abnormal ovarian growth pattern and hormonal imbalance is discussed.