Brain magnetic resonance imaging was conducted in a girl with genetically confirmed spinal muscular atrophy (SMA) type I. This patient has survived 6 years, to date, under mechanical ventilation. T2-weighted and fluid-attenuated inversion recovery images revealed high signal intensity lesions in the anterolateral portions of the bilateral thalami. Electroencephalography disclosed diffuse beta activity upon awakening and during light sleep. In addition, fast and prolonged spindles were observed. Although mild neuronal changes in the lateral nucleus of the thalamus have been described in several autopsied cases, this is the first study to demonstrate neuroradiologically and neurophysiologically the thalamic lesions in genetically confirmed SMA type I.