Among the genetics disorders, Down syndrome (DS) is the major cause of mental retardation, congenital heart and intestinal disease. So far, no certain therapeutic method has been suggested for the treatment of this syndrome. The aim of the current survey was to investigate the frequency of parental consanguinity, maternal age in the patients with DS.This study was conducted on 38 consecutive patients with clinically and laboratory confirmed DS who referred to the genetic lab of a referral University Hospital. The G-banding method for karyotyping was employed.The patients were 21 males and 17 females within the age of 16 days to 28 years old. Free trisomy (92.1%, n = 35) was the most common chromosomal abnormality. The frequency of DS was higher among the non-consanguine marriages (71.1%) in comparison with the consanguine marriages (28.9%). Mean age of the mothers in the consanguine marriages (mean = 27.1 ± 6.3) was lower than in the non-consanguine marriages (mean = 31.1 ± 7.7).Higher frequency of DS among the non-consanguine marriages in comparison with the consanguine marriages, may suggest that DS diagnostic tests might be done on all embryos regardless of the parents' familial relationship.