A 32-year-old Chinese woman presented for further investigation with a 6-year history of polyuria and polydipsia, a 4-year history of vulva ulceration and a 2-year history of gingival swelling. A biopsy of the vulva lesion showed diffuse infiltration of medium-sized cells with lobulated, grooved, vesicular nuclei. Occasional mitoses were present. The infiltrate of the cells showed reactivity with antibody to S-100 protein and CD1a, confirming the diagnosis of Langerhans' cell histiocytosis (LCH). Cephalic magnetic resonance imaging scanning revealed that an 8 × 7 × 8 mm3 large mass was located at the pituitary stalk. An X-ray film of the jaw showed sharply demarcated rarefaction of the right posterior portion of the mandible. In women with diabetes insipidus and genital ulcer, LCH should be considered in the differential diagnosis.