A ring 18 chromosome(18r) karyotype is a rare disorder characterized by short stature, obesity, microcephaly, mental retardation, micropenis, cryptorchidism, hypertelorism, epicanthal folds, micrognathia, and small hands with short tapering fingers. A 22-month-old girl was referred to our department of pediatrics because of ptosis and delayed development. Karyotype revealed ring 18 and dicentric ring 18 chromosome(46,XX,r(18)/45,XX,-18/46,XX,dic r(18)). Fluorescent in situ hybridization with 18 centromeric probe showed 18 ring chromosome with 1 signal and 18 dicentric ring chromosome with 2 signals. We report a case of a ring 18 chromosome diagnosed by karyotype and fluorescent in situ hybridization.