Cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy (CADASIL) is one of the most common hereditary forms of stroke, and migraine with aura, mood disorders, or dementia, are also frequently found in these patients. Missense mutations in the Notch3 gene that create or destroy cysteine residues, have been found in most cases with a family history of the disease, although a few sporadic cases harbouring Notch3 mutations have also been described. Here, we describe a 44‐year‐old patient with clinical features of CADASIL who was a carrier of a new Notch3 mutation: cys128→gly. Both parents were alive and healthy, and negative for the mutation. This case illustrates the interest of analysing the Notch3 gene in cases with clinical features of CADASIL, even in the absence of a family history of the disease.