Mutations in the smooth muscle-specific isoform of α-actin (ACTA2) cause vascular smooth muscle dysfunction leading to aortic aneurysm and moyamoya syndrome. A unique R179H mutation in ACTA2 has been reported to result in widespread smooth muscle dysfunction affecting vascular and extravascular smooth muscles. We report a 7-year-old girl with an ACTA2 R179H mutation manifesting with neonatal seizures due to multifocal infarcts, asymmetric motor deficits, global developmental delay, spasticity, congenital bilateral mydriasis, and a large patent ductus arteriosus. Serial magnetic resonance imaging (MRI) of the brain over 7 years showed diffuse supratentorial white matter abnormalities consistent with a progressive leukoencephalopathy. Magnetic resonance angiography of the cerebral vessels showed stenosis in the terminal portion of the bilateral internal carotid arteries with fusiform dilation of the proximal segment. Neonatal onset of neurologic symptoms in ACTA2 mutations has not been previously reported. R179H mutation in ACTA2 represents the severe end of the disease spectrum.