The pregnancy outcomes of 155 women who underwent an amniocentesis for a prenatal karyotype after being diagnosed by ultrasound as having one or more nonlethal structural anomalies are presented. Thirty-three (21%) patients were found to have an abnormal karyotype. Knowledge of the prenatal karyotype was useful in the subsequent management of these pregnancies. A pregnancy with a fetal anomaly diagnosed prior to 24 weeks was more likely to be terminated if an abnormal karyotype was also present. In women who were diagnosed as having a fetal anomaly with an abnormal karyotype at 24 weeks or later, only 3 of 13 (23%) infants survived the neonatal period. Knowledge of the karyotype results influenced decisions regarding the place, timing, and route of delivery in these fetuses. In 32 women, (21%) a karyotype was beneficial by avoiding maternal transport, cesarean delivery, and neonatal expenses at a Level III perinatal center. © 1991, by Thieme Medical Publishers, Inc. All rights reserved.