Eosinophils are one of the polymorphonuclear granulocytes derived from bone marrow stem cells, and they contain many small cytoplasmic granules that stain bright red with eosin or brick-red with Romanowsky staining. Eosinophilic infiltration is also present in various human central nervous system (CNS) diseases such as parasitic infection, transverse myelitis, vasculitis, Langerhans cell histiocytosis, glioblastoma and etc... Due to the morphologic and functional characteristics, the presence of eosinophils in certain lesions may provide useful diagnostic clues in the right clinical setting. Consideration of this finding may facilitate the diagnosis of CNS pathologic lesions, especially in a small specimen such as a stereotactic biopsy.