We present a case of sudden-onset aphasia due to a single pathological lesion, which at neuroradiological imaging studies was suggestive of glioma, while on biopsy proved be of demyelinating nature. Every cause of demyelinating lesions of the central nervous system was considered in the differential diagnosis, concluding for a primary demyelinating disease. The clinical and radiological differences between multiple sclerosis and acute disseminated encephalomyelitis are discussed. Although aphasia has already been described in demyelinating diseases, we underline its rarity as onset symptom.