Double trisomy is the presence of two numerical chromosomal abnormalities together. Since the most cases result in spontaneous abortus this is a rare situation. It generally arises by non-disjunction at either the first or second meiotic division. Down syndrome that is known as Trisomy 21 is the most common chromosomal aneuploidy and also the most common genetic reason of mental retardation. The case was sent to our laboratuary of medical genetics because of clinical features of Down syndrome. Conventional cytogenetic techniques were performed for this case. The karyotypes of our case were found as 48, XXX+21. The karyotypes of the parents were normal. In this study, it is aimed to discuss a rare double trisomy case and to compare our results with previous studies.