Tehran University of Medical Sciences Iranian Journal of Public Health 2251-6085 25 3-4 1996 09 15 1 4 D.D Farhud H. Sadighi H. Ameli A. Bagheri Z. Hosseini Mazhari 2015 10 03 Down’s syndrome, or 21 trisomy, is the most common autosomal abnormality, with incidence of 1 per 815 live births in Iran. Worldwide reports indicate that about 95% are regular trisomy, or nondisjunction, 1% are mosaic and 4% due to translocation. However, these values show a geographical variation. A cytogenetic study of Down's syndrome, or trismoy 21, was carried out on 366 cases (202 males and 164 females) during a 10 year period (1974-1983) in Akbarabadi maternity hospital in Tehran. The lymphocyte chromosomes were stained with G-banding technique. Free trisomy 21 constituted 93.44%, D/G translocation 3.55% and G/G translocation 3.01%. Reciprocal translocation and mosaic were not observed. The values are compared with other studies in some of the countries of the countries of the region. https://ijph.tums.ac.ir/index.php/ijph/article/view/1821 https://ijph.tums.ac.ir/index.php/ijph/article/download/1821/1802