A 24-year-old man was admitted for a painful gingival ulcer. Histology and immunohistochemistry of a lesional biopsy revealed the diagnosis of Langerhans cell histiocytosis (LCH). To rule out multifocal disease, a complete staging was performed. There was no evidence of bony lesions or any other organ involvement. The diagnosis of LCH restricted to the oral mucosa was established. The complete oral lesion was ablated by CO(2) laser and subsequently treated topically with triamcinolone acetonide. The patient is still in remission after one year of follow-up. LCH confined to the oral mucosa is rare. It presents usually as an inflammatory or ulcerative lesion, easily leading to misinterpretation and delayed diagnosis. Patients with limited unifocal mucocutaneous disease, as in the present case, usually have an excellent prognosis. However, the oral lesion may represent an early sign of LCH, predating and progressing to an aggressive life-threatening multiorgan disease.