Abstract In human beings, dicentric chromosomes are occasionally encountered as stable chromosomal constitution except Robertsonian translocations that occur in an insignificant portion of the population. In present investigation, an 18 years female born to younger parents, who was naturally delivered but was under wt. after birth and had 42, XX, tdic (2; 21) chromosomal constitution is described. It is suggested that the stability of dicentric chromosome has been attributed to inactivation of chromosome no. 2 centromere. Stanford-Binet test was performed to ascertain the degree of intellectual disability and was found to be severe (IQ: 20-25 to 35-40). A reciprocal translocation which leads to dicentric chromosome formed from a chromosome 2 and a 21chromosome has not apparently been reported in individuals with intellectual disabilities.