Eosinophilic ulcer of the oral mucosa is a benign lesion of unclear pathogenesis mostly affecting the tongue. It has been suggested to represent a reactive pattern to several stimuli. We report on a 12-year-old boy who presented with a painless infiltrating ulcer on the gingiva of the lower jaw, which was covered by necrotic yellowish slough. There were no pathologic features of the jawbones or regional lymph nodes. Histopathological, immunohistochemical and gene rearrangement studies were in agreement with eosinophilic ulcer with predominant oligoclonal CD3+ and CD30+ T lymphocytes expressing the Epstein-Barr virus membrane protein. The ulcer resolved within 4 weeks and follow-up for 3 years revealed no evidence of recurrence. Epstein-Barr virus may have played a role in triggering this reactive lymphoproliferative disorder.