Objective : Amniocentesis is the most prevailing procedures for prenatal cytogenetic analysis. We tried to elucidate the cytogenetic characteristics of amniocentesis performed in the Institute of Reproductive Medicine and Population, Seoul National University and the Department of Obstetrics and Gynecology, Seoul National University Hospital. Methods : From January 1994 to December 1999, transabdominal amniocentesis were performed for cytogenetic analysis in 1738 patients. Results : The most frequent indication for amniocentesis was advanced maternal age(43.4%, 755/1738) and the next was abnormal serum marker(31.7%, 552/1738). The overall incidence of abnormal karyotyping results was 5.4%(97/1788). We showed that the incidence of abnormal karyotyping was different according to its own indication (Pearson chi-square test, p<0.001). Conclusion : The indication for genetic amniocentesis is an important factor to predict anticipated abnormal results.