Information concerning the observation of 231 children with Down’s syndrome with mothers under 37 of age at their birth has been studied.

These children along with others with the same or another abnormalities were kept at special centers in different cities of Iran.

This information includes sex and parental age of the children at their birth. The frequency of these children has been studied with regard to their paternal age groups. A careful study of the results through direct adjusted rates method showed that old age of the father increases the risk of the appearance of Down’s syndrome in the offspring. This risk is mostly directed towards the male children.