Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a small-to-medium-sized vessel disease that causes degeneration of vascular smooth muscles. The most frequently found mutation is NOTCH3 on chromosome 19, the presence of which confirms the diagnosis of CADASIL. The core features of CADASIL are migraine, ischemic events, cognitive decline, and psychiatric features. Its symptoms overlap with other diseases, most commonly with multiple sclerosis (MS). Both diseases can give fluid-attenuated inversion recovery in periventricular regions and deep white matter. CADASIL is often misdiagnosed and treated as MS due to these similarities. We present a case of a 28-year-old woman who began treatment for MS and was later confirmed with a diagnosis of CADASIL with a NOTCH3 mutation.