We report the case of a 27 year-old man developing recurrent oral aphtosis associated with fever and 8 kg of weight loss. Moderate splenomegaly was observed on physical examination and neurological and cardiac examination were normal. Laboratory findings included marked eosinophilia at 3280 giga/l. Bone marrow (BM) examination revealed a myeloproliferative syndrome with mature eosinophils. Splenectomy was performed because of a suspected nodule on the BM, the histopathology revealed a myeloid metaplasia. The diagnosis of myeloproliferative form of hypereosinophilic syndrome (HES) was made. He was treated with interferon-alfa and hydroxyurea. After two years of treatment he had no ulcer recurrence and eosinophil count was at 180 giga/l. Mucosal manifestations as a prodromal symptom of HES are rare. The histology of the lesions shows numerous eosinophils; immunohistochemical analysis confirms the presence of eosinophil peroxydase, major basic protein and eosinophil derived neurotoxin. A few cases have been described. Death occurs 11 months to 5 years after the diagnosis of oral ulcerations. The treatment consists of interferon-alfa and hydroxyurea.