Introduction: Holoprosencephaly (HPE) is a rare presentation in newborns. It refers to an incomplete or absent division of the prosencephalon or forebrain into distinct cerebral hemispheres. Case presentation: A preterm baby girl, first of dizygotic twins, born at 26 weeks of gestation to a 45 year old mother, was prenatally diagnosed with ventriculomegaly on fetal ultrasonogram. At birth the baby had frontal bossing with sun setting eyes and a full anterior fontanel. Initial head ultrasonography (HUS) showed ventriculomegaly and semilobar holoprosencephaly, which was confirmed by computed tomography scan. Subsequently, the baby developed hydrocephalus that progressively increased. Eventually, the cerebrospinal fluid required drainage and a ventriculoperitoneal shunt was placed. Conclusion: Holoprosencephaly has heterogeneous etiologies, including teratogenic and or a genetic basis. It is prudent to diagnose holoprosencephaly prenatally and determine the type to classify severity, complications and survival rate. It is also important to recognize that even with monozygotic twins only one twin may have HPE. The parents of a baby diagnosed with holoprosencephaly should be counseled about the poor prognosis.