Objective:To better understand the karyotype distribution ofthe patients with Down’s syndrome(DS)who have been finally diagnosed in our hospital.To compare the strengths of G-banding karyotype analysis and FISH(Fluorescence In Situ Hybridization

FISH)in diagnosing the DS patients with the Chromosome mosaicism and Calculating the percentage of abnormal karyotypes.Methods:Blood of the patients who were likely to suffer from DS was selected for G-banding karyotype analysis to describe the karyotype distribution.5 of the finally diagnosed patients with the chromosome mosaicism were randomly selected for FISH to compare the percentage of abnormal karyotypes of the two methods.Results:287 DS patients were diagnosed

91.29%of whom had the simple karyotype.Among the patients with the translocation karyotype

11 D/G translocation karyotype were detected

accounting for 73.33%

while 4 G/G translocation karyotype were diagnosed

constituting 26.67%.One patient with both of the translocation karyotype and the mosaicism karyotype was detected in our research

which was uncommon in recent report.The results of FISH and G-banding karyotype analysis were consistent.There was no significant difference of the abnormal karyotype rates for DS patients with the chromosome mosaicism by G-banding karyotype analysis and FISH.Conclusion:The simple karyotype is the main karyotype of the DS patients in our research.Among the translocation karyotype

the D/G kind is common.DS patients can be diagnosed efficiently by G-banding karyotype analysis

but we still suggest to use FISH to get the proportion of the abnormal cell for the patients who have less triploid cell and slighter clinical manifestation.