Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a genetic disease characterized by ischemic stroke with early onset, migraine, seizures, and vascular dementia. CADASIL is associated with mutations within NOCT3 gene, mainly clustered in exons 3 and 4. We report a case of CADASIL presenting progressive subcortical dementia in the sixth decade. Neither family history, nor acute ischemic events were present. MRI findings were typical for CADASIL. NOTCH3 analysis disclosed a new missense mutation within exon 7, leading to the substitution of cysteine 366 with a tryptophan (Cys366Trp). Our finding suggests CADASIL diagnosis must be considered in patients with vascular dementia also in absence of stroke-like events and of family history.