OBJECTIVE: The aims of this study were 1) to evaluate the indications of chorionic villus sampling CVS) and the positive predictive value for fetal chromosomal abnormalities, 2) to evaluate the reliability of CVS at Asan Medical Center, 3) to find out the risk factors of procedure-related fetal loss, 4) to find out the risk factors of culture failure, and 5) to compare transabdominal with transvaginal approaches. METHODS: Medical records of the 429 out of 461 patients in whom the CVS for prenatal cytogenetic diagnosis were performed were reviewed retrospectively for the period of June 1998 to June 2006. RESULTS: (1) The most common indications of CVS were abnormal ultrasonic findings including increased nuchal translucency (153/429, 35.7%), a previous history of cytogenetically abnormal baby (125/429, 29.1%), old maternal age (100/429, 23.3%), family history of genetic disease (22/429, 5.1 %), and parental abnormal karyotype (11/429, 2.6%). (2) The positive predictive value of abnormal karyotyping according to the indication of CVS was highest in the cases showing abnormal USG findings, including increased fetal nuchal translucency (28.3%). (3) The trial success rate of CVS was 99.5%(427/429). Culture failure rate was 1.9%.(4) Of the 427 cases, normal karyotype was revealed in 349 cases (81.7%), abnormal karyotype in 66 cases (15.2%), maternal cell contamination in 6 cases (1.4%), and pseudomosaicism and confined placental mosaicism (CPM) in 6 cases (1.4%). (5) Procedure-related fetal loss rate was 1.6% (7/419). (6) The significant risk factor of fetal loss was presence of preprocedure vaginal bleeding. (7) The significant risk factor of culture failure was a small amount (less than 10 mg) of tissue. (8) The gestational age at procedure was significantly different between transabdominal and transvaginal methods. In the transabdominal approach group, the incidence of fundal location of placenta was significantly more common. CONCLUSION: If CVS is performed by an expert operator and at a good quality of genetic laboratory, CVS is a very safe and reliable procedure for prenatal genetic diagnosis.