There are some developmental disorders children with distinctive facies or unusual behaviors in pediatric developmental clinic.Doctors can learn the differential diagnosis from their distinctive facies or unusual behaviors just like Down syndrome.William syndrome,Cornelia De Lange syndrome,fragile X syndrome,Rett syndrome,DiGeorge syndrome and Prader-Willi syndrome are the common developmental disorders with distinctive facies or unusual behaviors.Williams syndrome should be noted among hyperaction children.Except for hyperaction,Williams syndrome children also show excessively lively and enthusiastic behavior with the distinctive facies of periorbital fullness,malar flattening,long philtrum,wide mouth and short nose.DiGeorge syndrome can be found among delayed speech or dysarthria children.Palatopharyngeal dysfunction,learning disabilities and facial abnormalities,such as small jaw,low ear and abnormal auricle,can also be found meanwhile.Williams syndrome and DiGeorge syndrome can be diagnosed by the MLPA or array- CGH technology with 7q11.2 and 22q11.2 microdeletion respectively.Cornelia de Lange syndrome should be noted among developmental retardation or short stature children.Meanwhile,distinctive facies also can be found,such as synophrys,arched eyebrows,long curve and dense eyelashes,hairy forehead,short nose,long philtrum.This disease can be diagnosed by the analysis of NIPBL gene,SMC1A gene,SMC3 gene,RAD21 gene and HDAC8 gene,of which the NIPBL gene mutations are above 50%.Fragile X syndrome should be noted in the males of autism or mental retardation,and it is with the distinctive facial features,including long face,large ears,prominent forehead,prominent jaw,large mouth and high palatine arch.It can be diagnosed by FMR1 gene analysis.Rett syndrome should be alert in female autism with development retardation or retrogression.It is characterized by stereotypic movements of the hands,including wring hands,claping hands,beating,biting hands and rubbing hands.It can be done by MECP2 gene analysis.Prader-Willi syndrome should be paid attention to among malnutrition,growth failure or development retardation in the early life or obesity during childhood.In addition,distinctive facial features also can be found,including long head,narrow bifrontal diameter,almond-shaped eyes,small mouth,thin upper lip,downward angulus oris.It is caused by the deletion of the paternal copies of the imprinted genes within the chromosome region 15q11-q13,and MS-MLPA technology can be used for diagnosis.