The authors report a wide and updated revision of hydranencephaly, including a literature review, and present the case of a patient affected by this condition, still alive at 36 months.Hydranencephaly is an isolated and with a severe prognosis abnormality, affecting the cerebral mantle. In this condition, the cerebral hemispheres are completely or almost completely absent and are replaced by a membranous sac filled with cerebrospinal fluid. Midbrain is usually not involved. Hydranencephaly is a relatively rare cerebral disorder. Differential diagnosis is mainly relevant when considering severe hydrocephalus, poroencephalic cyst and alobar holoprosencephaly. Ethical questions related to the correct criteria for the surgical treatment are also discussed.