Subependymal giant cell astrocytomas are one of the three major intracranial lesions found in tuberous sclerosis complex. Subependymal giant cell astrocytomas are typically slow-growing tumors of mixed glioneuronal lineage which can become aggressive and cause obstructive hydrocephalus usually in older children and adolescents. Neonatal subependymal giant cell astrocytomas are extremely rare, and their natural history and prognosis are poorly understood. This report investigates an extremely large neonatal subependymal giant cell astrocytoma which was initially identified in utero at 19 weeks of gestation in a high-risk pregnancy with no family history of tuberous sclerosis complex.