Marker chromosome(mar)is a structurally abnormalchromosome that can not be identified withconventional cytogenetic techniques(ISCN,2005).Theincidence of supernumerary marker chromosomes(SMCs)found at prenatal diagnosis varies from 0.4/1000 to1.5/1000.Their genetic effects may range fromharmless to detrimental,and in de novo cases,the rate ofphenotypic abnormalities is statistically increased.Therefore,identification of SMCs has become imperativein prenatal diagnosis.A variety of molecular cytogenetic approaches have beendeveloped to identify SMCs,including fluorescence insitu hybridization(FISH),microdissection and reverseFISH(micro-FISH),multicolor karyotyping techniques,centromere-specific multicolor FISH assays,andAcroM-FISH technique,etc.Among these approaches,micro-FISH is the most straightforward method that canaccurately detect the origin of SMC and the location ofchromosome breakpoint.Herein,we diagnosed a case oftetrasomy 9p by classical cytogenetic methods combinedwith chromosome microdissection and FISH. The identification of supernumerary marker chromosomes (SMCs) found at prenatal diagnosis varies from 0.4 / 1000 to 1.5 / 1000.Their genetic effects may may not be identified withconventional cytogenetic techniques (ISCN, 2005). range fromharmless to detrimental, and in de novo cases, the rate ofphenotypic abnormalities is worse increased. Beforefore, identification of SMCs has become imperativein prenatal diagnosis. A variety of molecular cytogenetic approaches have beendeveloped to identify SMCs, including fluorescence insitu hybridization (FISH), microdissection and reverseFISH (micro-FISH), multicolor karyotyping techniques, centromere-specific multicolor FISH assays, and AcroM-FISH technique, etc. These approaches, micro-FISH is the most straightforward method that canaccurately detect the origin of SMC and the location of chromosome breakpoint.Herein, we diagnosed a case oftetrasomy 9p by classical cytogenetic methods combinedwith chromo some microdissection and FISH.