Objective: To systematic analyze the change of indications, age distribution of the patients and chromosomal results according to patient's age and indications in midtrimester genetic amniocentesis Methods: This study reviewed 2,000 genetic amniocentesis cases from 1984 to 1997 which were done at Severance Hospital, after prenatal genetic counseling for the mothers who have high risk for carrying chromosomally abnormal babies. We analized the change of the indication, age distribution and chromosomal results according to maternal age and indications of amniocentesis Results: 1. The incidence of amniocentesis had been in gradual increase since the 1980's, and from the mid 1990's it showed an abrupt increment. 2. Of the 2,000 amniocentesis cases, 31.8% was maternal age 35 to 39 which was most common age group and followed by age 30 to 34 was 28.4% and age 25 to 29 was 27.4. 3. The indications for amniocentesis were advanced maternal age(39.6%), abnormal maternal serum markers(27.8%) and abnormal ultrasonographic findings which implies chromosomal abnormality(6.4%). Recently maternal serum markers and ultrasonography play an important role as an indicator for the amniocentesis. 4. From the 2000cases, 1,950 cases showed normal diploidy and 50 cases abnormal karyotype which consisted 2.5%. In autosomal disorders ll Down syndrome, 7 Edward syndrome, 1 Patau syndrome, 15 Translocation, 3 Mosaicism were diagnosed. In sex chromosomal disorders 3 Klinefelter syndmme, 2 Turner syndrome and other 8 chromosomal abnormalities were diagnosed. No statistic significance was found among different age groups. Those who had abnormal ultrasonographic findings implying chromosomal abnormality were found to have correlation with chromosomal abnormality than other indications Conclusion: Midtrimester genetic amniocentesis is an important diagnostic tool in prenatal diagnosis, of which the annual incidence has been recently increased abruptly. Not only maternal age, but the maternal serum markers and ultrasonograms should be considered in prenatal counseling, The genetic amniocentesis should be well informed to the general population.