Cysts of the choroid plexus have been identified ultrasonographically in second-trimester fetuses and usually have regressed by 24 weeks' gestation. Choroid plexus cysts have been linked with trisomy 18, and this possible association has prompted a review of our experience. Choroid plexus cysts were seen ultrasonographically in 38 consecutive fetuses between 15 and 28 weeks' gestation. Of these, 30 underwent repeat ultrasonograms after 24 weeks' gestation and showed complete resolution of the cysts. In 10 of the 38 fetuses, amniocentesis yielded normal karyotypes. A total of 36 patients were delivered of normal neonates at term. One patient was delivered of a normal neonate prematurely, at 34 weeks' gestation with a good outcome. Another fetus was delivered at 36 weeks' gestation because of late onset of nonimmune hydrops, which resolved without sequelae. No association between trisomy 18 and choroid plexus cysts was identified in this series.