The adult-onset Alexander disease (AOAD) dramatically differs from the early onset AD with respect to clinical and neuroradiological findings. Herein we report the detailed clinical and neuroradiological findings of a Turkish family with AOAD. In all three cases, magnetic resonance imaging revealed marked atrophy of the mesencephalon, bulbus, and cervical spinal cord accompanied with signal abnormalities in the same regions along with supratentorial white matter. Basal ganglia were affected in two cases. Molecular genetic analysis revealed heterozygous mutation in the 8th exon of the glial fibrillary acidic protein gene M451I (c.1245G>A), leading to the diagnosis of AOAD in all cases.