Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a rare genetic disorder due to a NOTCH 3 mutation on chromosome 19 resulting in a small vessel disease that may mimic many other neurological disorders like migraine, stroke, transient ischaemic attack (TIA), dementia and psychiatric illnesses. The gene discussed is NOTCH3; the disease is dementia.