The Down syndrome (DS) is the well-known trisomy, which is caused by additional copy ofchromosome 21.There are three types of DS. First, fully trisomy (47,XY,+21or 47,XX,+21).Second, translocation DS which result as translocation between chromosome 14 and21(46,XY,trans (14:21) or (46,XX,trans (14:21)). And the third type the mosaic DS that two celllines present in the individual. Mostly, studies indicate that frequency of each type 95%, 4% and1% respectively. Our study aims to estimate the frequency of each of the three types of DSchromosomal abnormalities in Iraqi samples. Chromosomal analysis using G-band technique wasperformed for 200 Down syndrome cases and 168 of their parents (whenever there were mosaicDS cases their parents were submitted chromosomal analysis). Fifty-seven percentage of caseswere fully Trisomy, forty-three percentage of them were mosaic DS, and no translocation patternwas recorded. The maternal ages were between 25-45 for the mosaic DS mothers. According tothis study, the frequency of mosaic DS was varied. It seems more investigations need to be donefor larger number of DS, and the impact of environmental changes in last decades need to bestudied more to be sure of its role in increasing of the proportion of this type of Down syndrome.