Megalencephalic leukoencephalopathy with subcortical cysts is an autosomal recessive cerebral white-matter disorder in children. Megalencephalic leukoencephalopathy with subcortical cysts is caused by mutation in the megalencephalic leukoencephalopathy with subcortical cysts gene 1. The authors report a case of a 2-year-old Tunisian boy who had presented seizure following minor head trauma. He had megalencephaly, cerebellar ataxia, and mild pyramidal signs at physical examination. Magnetic resonance imaging showed extensive white-matter signal changes involving the corpus callosum and temporal subcortical cysts consistent with megalencephalic leukoencephalopathy with subcortical cysts. The molecular genetic study of the megalencephalic leukoencephalopathy with subcortical cysts gene 1 identified a homozygous mutation C46fsX57 in the patient. The mutation was found to be heterozygous in the parents. To the best of the authors' knowledge, this mutation has never been reported.