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Cytogenetic studies were carried out on all the live-borns diagnosed clinically as Down’s syndrome born at the University Hospital at Mansoura in the period January 1978-April 1983. Also 236 cases of Down’s syndrome not delivered in our Hospital but referred to the Genetics Unit within the same period, were examined and recorded. The Giemsa-Trypsin banding technique was used for cytogenetic examination. The incidence of Down syndrome was 1 in 555 livebirths from a total of 17762 such births. The mean age of mothers having liveborns with Down syndrome was 29.1 and of mothers of Down syndrome cases referred to the clinic was 29.8. The mean age of fathers of the first group was 34 and of the second group was 35.8. The distribution of the maternal and paternal ages showed a peak of incidence at maternal age 25-34 and at paternal age 30-39. Cytogenetic studies revealed that in the liveborns 27 (84.3%) were complete trisomy 21, 4 (12.4%) were mosaic, and 1 (3.1%) was translocation. In the 236 referred cases 201 (85.1%) were complete trisomy 21, 32 (13.5%) were mosaic, and 3 (1.2%) were translocation. The sex ratio (M/F) was found to be 1.28 in the liveborns and 1.14 in the referred cases.