Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an identifiable cause of inherited stroke among young adults, characterised by diffuse leukoencephalopathy with prominent involvement of the temporal poles and external capsule. The disease is caused by mutations in the NOTCH3 gene encoding a NOTCH3 receptor protein. The clinical course is relentlessly progressive with early transient ischaemic attacks (TIA) or strokes, dementia and finally death in the mid-60s. We describe a 40-year-old patient with clinical features of CADASIL and a positive family history who was a carrier of a new mutation at the exon 4 of the NOTCH3 gene: C162R. Regardless of the distinctive clinical and neuroimaging features one of his siblings had been mistakenly diagnosed as suffering from multiple sclerosis (MS), suggesting that the disease can occasionally be misdiagnosed as MS.