Eosinophilic ulcer demonstrates a rapid onset, with some weeks of duration before spontaneous regression. The exact pathogenesis of eosinophilic ulcer is still poorly understood, and different etiologies have been proposed. It is microscopically characterized by the presence of a dense inflammatory infiltrate containing a large number of eosinophils that more often surround muscular fibers. The inflammatory component is mainly composed of cytotoxic T lymphocytes, mast cells, and macrophages; and the presence of a few large atypical cells positive for CD30 as either scattered or clustered infiltrates led some authors to hypothesize the possibility that this lesion represents a spectrum of the CD30+ lymphoproliferative disorders affecting the oral cavity. Any mucosal location of the oral cavity can be affected, especially the tongue, more often as an asymptomatic, solitary, persistent ulcer. The lesion exhibits variable size and shape, with large ulcers with central areas covered by a yellowish fibrinopurulent pseudomembrane, and because of its elevated and indurated borders, eosinophilic ulcers may strongly resemble squamous cell carcinoma. Although eosinophilic ulcers commonly demonstrate benign and self-limited behavior, biopsy should be considered in persistent lesions. After biopsy the lesions usually heal in 1–2 weeks and recurrences are uncommon.