Alobar holoprosencephaly is an intracranial abnormality characterized by fa
ilure of proper cleavage of the prosencephalon, accompanied by incomplete m
idfacial development. The prenatal sonographic diagnosis of alobar holopros
encephaly was first described in 1984; however, there have been only two re
ports of alobar holoprosencephaly diagnosed in the first trimester. We repo
rt a case of alobar holoprosencephaly diagnosed at 10 weeks of gestation.