This case history reports on the second family in Denmark to be diagnosed with CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy). Due to symptoms, signs and paraclinical findings, an initial diagnosis of multiple sclerosis was made. However, MRI findings of leucoencephalopathy in the external capsule and anterior temporal lobes together with negative CSF findings and family history raised suspicions of CADASIL. Skin biopsy with granular osmiophilic material (GOM) and genetic testing showing the NOTCH 3 mutation proved the diagnosis. There is considerable variability in the symptoms of CADASIL; however, most often a family history of migraine, cerebrovascular events and dementia in early life is found.