RNASET2-deficient cystic leukoencephalopathy also called ‘RNASET2 deficiency’ or ‘cystic leukoencephalopathy without megalencephaly’ denotes a rare neurogenetic condition that follows an autosomal recessive inheritance. The prevalence is unknown. So far 14 mutation positive cases have been reported. Affected individuals develop psychomotor impairment, spasticity, and epilepsy in early infancy. Brain magnetic resonance imaging (MRI) reveals frontal and temporal lobe cystic lesions, multifocal white matter alterations, and cerebral atrophy. Cranial computed tomography (CT) scans depict intracranial calcifications in some affected individuals. In severe cases, clinical and neuroradilogical abnormalities are already present shortly after birth followed by a seemingly non-progressive clinical course, suggesting that the active phase of the disease and the main cerebral damage occur during fetal brain development. These phenotypic features are indistinguishable from the sequelae of in utero cytomegalovirus (CMV) brain infection. Moreover, there is a significant clinical, biochemical and neuroradiological overlap of RNASET2-deficient cystic leukoencephalopathy with Aicardi-Goutières syndrome (AGS) in some affected individuals.