A case of parabiotic twin pregnancy is described with early fetal co-twin loss and topical isocortical disruption and gastroschisis in the surviving twin. We conclude from this case that early fetal parabiotic twin syndrome (before 16 weeks of gestational age) may cause microgyria and neuronal heterotopia. The cerebral and extracranial findings can be explained as the result of multiple vascular obstructions. Whereas most cases of parabiotic twin syndrome with brain damage involve cystic necrosis, focal hypoplasia with disrupted development in the affected part has been found in the present case. The probable reason in discussed. The roentgenographic analysis of the dead twin fetus is consistent with the period of 13-16 weeks as the likely period in which microgyria and neuronal heterotopia originated in the surviving twin. The present case constitutes one of the rare instances in which neuronal migration disturbance in the human could be dated reliably.