Amniocentesis was performed for prenatal diagnosis in 407 pregnancies between the gestational ages of 11-14 weeks. The safety and accuracy of the procedure were compared with data obtained from collaborative studies of amniocentesis performed later in the second trimester. There were no differences observed with respect to accuracy, pseudomosaicism, or maternal-cell contamination related to the timing of the procedure. The fetal loss rate within 4 weeks of the procedure was 2.3%. Fetal losses appeared to be related to maternal complications such as bleeding and leakage of fluid that occurred within a day of the procedure. No major maternal complications were noted. Information regarding neonatal outcome, including pulmonary complications and congenital orthopedic postural deformities, was found to be similar to that in previous reports.