A 62-year-old woman had progressive dysarthria for 2 months and was suspected of having amyotrophic lateral sclerosis because of the presentation of bilateral tongue atrophy and fasciculation. Brain magnetic resonance imaging (MRI) showed enlargement of the left hypoglossal nerve, and whole-body gallium scintigraphy showed abnormal uptake in the left pelvic cavity and left thigh. On the basis of the findings of biopsy of the mass lesion in the left thigh, she was diagnosed with diffuse large B-cell lymphoma. After chemotherapy for diffuse large B-cell lymphoma, the tongue atrophy improved. The patient subsequently developed left oculomotor nerve palsy, weakness of the right arm, and weakness of the right leg. The cause of these symptoms was thought to be neurolymphomatosis on the basis of the typical MRI findings observed. We report a rare case of neurolymphomatosis presenting as bilateral tongue atrophy, mimicking amyotrophic lateral sclerosis.