The simple technique of ultrasound guided transabdominal choriocentesis allows rapid karyotyping early in the second trimester. Choriocentesis was carried out in 147 pregnancies at (genetic) risk during the 13th-19th week of gestation. Results of reliable karyotyping were available within 2-4 days. In 146 (99.3%) women a sufficient amount of chorionic villi could be collected with maximal two needle insertions. An abnormal karyotype was found in four pregnancies, which were terminated selectively on parental request. In all pregnancies a follow-up by ultrasound was performed 4 weeks after the procedure, one (0.7%) unexplained fetal death occurred, 143 pregnancies remained uneventful. We concluded that transabdominal choriocentesis is a simple rapid and relatively safe method, which can be useful for rapid karyotyping during the second trimester.