The antenatal appearance of gastrointestinal duplication cysts is desc
ribed. Two cases are presented: a duplication cyst of the pylorus and
a cyst of the terminal ileum. The embryogenesis and the clinical utili
ty of prenatal diagnosis of these malformations of the alimentary trac
t are discussed. Antenatal detection of these cystic masses allowed cl
ose neonatal surveillance and timely surgical intervention prior to ne
onatal complications.