The paper deals with first trimester diagnosis of exencephaly. In association 
with first trimester sonographic and cytogenetic screening of chromosomal 
anomalies in 1145 examined pregnancies 2 exencephalic fetuses with normal 
karyotype were diagnosed. Exencephaly was characterized with the absence of 
normal echoes of the exocranium, the lateral ventricles, the chorioid plexus, 
the cerebral falx, and with the presence of deformed shape of the head and 
irregular, lobulated cerebral material with increasing volume at follow-up 
examination. Anencephalic fetuses were diagnosed subsequent to therapeutic 
abortion, since the uterine and cervical wall contractions eroded the fragile 
brain tissue during fetal expulsion. However, fetal brain was identified in 
abortion material in both cases providing evidence that exencephaly is an 
embryologic precursor of anencephaly.