Acardia is the most severe complication in monozygotic twinning. Acardius acormus is an uncommon phenotype among acardias. We report on an acardius acormus using thorough gross and light microscopic examination of the brain. Neuropathological examination revealed a severely disorganized cerebral cortex, agenesis of cerebellum and brain stem, and undeveloped basal ganglia and thalamus. In particular, the cerebral cortex was characterized by no clear lamination, almost complete loss of neurons, extensive gliosis, angiogenesis and focal mineralization. Neurohistology of the acardius acormus clearly demonstrated two types of lesions: developmental arrest of the brain and hypoxic-asphyxic damage to the brain with reactive gliosis and angiogenesis. Both types of lesions may be induced by the same teratogen: early onset of persisting hypoxia due to a reversed arterial perfusion. The quality of the description contributes valuably to a better understanding of the basic mechanism underlying the acardius phenotype.