Very echogenic amniotic fluid has been variably attributed to meconium, blood, or vernix caseosa. However, most previous reports have been case reports, and most cases have not had proof by amniocentesis. In a larger series of patients with proof by amniocentesis, we sought to determine the relative frequency of these substances as causes of very echogenic amniotic fluid. We retrospectively identified obstetric sonograms in which the amniotic fluid was homogeneously filled with innumerable echogenic particles. The cause of the increased echogenicity was determined by fluid appearance at amniocentesis. Of 86 cases identified, immediate proof by amniocentesis was available in 19 patients for whom the gestational age ranged from 32.8 to 39.4 weeks. Vernix was present in 18 (95%) patients and meconium in one (5%) patient. Very echogenic amniotic fluid in the third trimester is most often due to vernix and infrequently due to meconium. This sonographic finding is not a reliable indicator of meconium or blood in amniotic fluid and should not typically alter antenatal management.