Holoprosencephaly is a rare brain abnormality resulting from an incomplete 
cleavage of the primitive prosencephalon of forebrain during early 
embryogenesis. It includes a series of rare complex and heterogenosis disorders. 
Alobar form is associated with an extremely poor fetal prognosis. Here we report 
three cases of alobar holoprosencephaly and one case of semilobar 
holoprosencephaly diagnosed at the third trimester. Causes, diagnosis and 
management of holoprosencephaly are discussed referring to literature.