Amyotropic lateral sclerosis(ALS) is a progressive degenerative illness of unknown cause ; we present its characteristic brain magnetic resonance(MR) findings in one patient. A 58-year-old woman who for two years had been suffering from progressive motor weakness and dysarthria was admitted to our hospital. Physical examination and laboratory findings showed a pattern of both upper and lower motor neuron disease such as decreased motor power(Grade III), tongue atropy, increased deep tendon reflex, a pattern of lower motor neuron disease, as seen on electromyogram, and a pattern of sparing sensory nervous system, extraocular muscle movement bladder, and bowel function. On axial brain MR proton-density and T2-weighted images, small round areas of high signal intensity were seen bilaterally in the posterior limb of the internal capsule ; these corresponded to the corticospinal tract. Additionally, bilateral, subtle linear low signal intensity in the precentral gyrus was noted on T2-weighted imaging. On the basis of the findings of clinical and laboratory examination, and of typical MR imaging findings, ALS was diagnosed.