RESUMO
Holoprosencephaly is a rare malformation encountered in newborns. It refers to the absent or incomplete division of the prosencephalon.Case no. 1: a fetus was diagnosed by ultrasonogram at 29 weeks of gestation with alobar holoprosencephaly, proboscis and cyclopia. The premature infant was delivered by cesarean section at 32 weeks of gestation, confirming antenatal diagnosis.Case no. 2: a premature newborn at 29 weeks of gestation, who presented posterior pole of cranial cavity occupied by a translucent, asymmetrically disposed structure, with anatomically normal cerebellum, compressing the posterior horn of the left cerebral hemisphere. Lateral ventricles, had also a large communication in their middle with incomplete fused thalami. The diagnosis of lobar holoprosencephaly with arachnoid cyst was confirmed by the autopsy.