Holoprosencephaly is usually associated with microcephaly, although macrocephaly is not uncommonly seen. However, the cause of hydrocephalus in holoprosencephaly remains ill-defined. Here, the authors report a case of CSF ascites following ventriculoperitoneal shunt placement in a five month-old child with alobar holoprosencephaly, and hypothesize that the excessive CSF production which occurs in this condition may be responsible for the formation of CSF ascites. Further research is required to assess whether the gene responsible for holoprosencephaly is also responsible for upregulating CSF production in patients with concomitant hydrocephalus.