Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL; OMIM #125310) is the most common cause of monogenic familial cerebral small vessel disease. It typically manifests at middle adulthood with highly variable clinical features including migraine with aura, recurrent transient ischemic attacks or ischemic strokes, mood disorders, and progressive cognitive decline. It is caused by mutations in the NOTCH3 gene, which maps to the short arm of chromosome 19 and encode for epidermal growth factor-like repeats. In this article, we report a 40-year-old male patient who presented with a two-year history of progressive cognitive decline including impaired attention, memory, executive functions, and processing speed whose family history was strongly positive for young-onset ischemic stroke and memory impairment. His father, uncle, and grandfather died due to ischemic strokes and cognitive impairment (similar condition). A whole exome sequencing to the patient (proband II-1) revealed a novel heterozygous missense variant c.3009G>T, p.(Trp1003Cys) (chr19;15291625; hg19) in exon 19 of the NOTCH3 gene. Sanger sequencing was used to confirm the variant in other family members. This variant has not been described in the literature so far. The novel mutation described in the present study widened the genetic spectrum of NOTCH3-associated diseases, which will benefit studies addressing this disease in the future. CADASIL remains a disabling disorder leading to medical retirement in our patient due to late clinical presentation, lack of family history taking prior to joining the military, and lack of curative therapy. Further research for therapeutic options is needed including stem cell therapy .