Some recent reports have suggested that invasive testing is unnecessary when ultrasound either confirms or refutes a neural tube defect (NTD). However, counseling for recurrence risks and the possibilities for in utero therapy would be significantly altered by an aneuploid karyotype. We report our experience with 53 pregnancies affected by NTD in which we found 13.2% of these fetuses with abnormal chromosomes. In view of the higher than previously published incidence of aneuploidy, we.believe that fetal karyotypes are essential in the evaluation of all fetuses with NTDs.