Partial duplication of 3q is a rare chromosomal disorder that leads to multiple congenital abnormalities such as growth retardation, microcephaly and characteristic facial features. Although the phenotype of the patient has similarities with Cornelia de Lange Syndrome they are etiologically different. We report here a 9 months old baby boy with partial duplication of 3q and features similar with Cornelia De Lange syndrome. Conventional cytogenetic analysis revealed a derivative chromosome 21. In order to determine the origin of this chromosome region we used subtelomeric FISH technique. Based on the results of all these cytogenetic studies and the physical examinations, the diagnosis is partial 3q duplication.