Eosinophilic ulcer of the oral mucosa (EUOM) is an uncommon self-limited oral condition that clinically manifests as a solitary ulceration with elevated indurate borders affecting the tongue, buccal mucosa or lip. Microscopically, it is characterized by a polymorphic inflammatory infiltrate with a prominent polymorphonuclear eosinophilic component extending deep into the submucosa, underlying muscle and salivary glands. Large mononuclear cells probably corresponding to histiocytes, myofibroblasts or activated lymphoid cells are also frequently observed. The exact pathogenetic mechanisms implicated in the development of EUOM are poorly understood; however, the possibility that trauma may play a role in its development has been often postulated. Since its original description, the possibility that EUOM could be either considered an individualized disorder or a non-specific reactive pattern secondary to several stimuli has been discussed. EOUM may show some overlapping features with some entities such as atypical histiocytic granuloma, mucosal angiolymphoid hyperplasia with eosinophilia, and Kimura disease. The clinical and histopathological features and the differential diagnosis of EUOM are reviewed and its existence as a distinct disease discussed.