Langerhans' cell histiocytosis (LCH) is a neoplastic disease due to uncontrolled proliferation of Langerhans' cells (LCs); damage to organs involved appears to be due to the various cytokines secreted. The true cause of LCH remains a mystery. LCH can present at any age; there is female predominance and the skin is often the first site to be involved. Scaly papules, vesicles, purpuric nodules, plaques and ulcers are the main diverse presentations typically found on the scalp, flexures (including the perineum), crease below the breast, palms, soles and nails. The patient described here is a 35-year-old Saudi Arabian woman with a vulval ulcer that had been misdiagnosed as an infective lesion 11 months before the correct diagnosis of LCH was made by means of biopsy examination. Diffuse infiltration of LCs with large pale reniform/convoluted nuclei and abundant amphophilic cytoplasm in the company of neutrophils, eosinophils, lymphocytes and plasma cells were observed on light microscopy. Immunohistochemical staining, indicating S100 protein positivity in LCs and the demonstration of Birbeck granules by means of electron microscopy, confirmed the diagnosis. The 'skin-only' LCH may later progress to involve other organs; alternatively skin lesions may be part of the multisystem, disseminated disease. There is need for careful follow-up of all LCH patients, as the course of the disease cannot be reliably predicted from either the clinical presentation or histology of the lesion. In many cases the prognosis is good, there being limited involvement that does not progress. Surgery or local steroids might suffice as therapy. However, for severely symptomatic disease, in which there are complications associated with dysfunction (or failure) of vital organs such as the liver, lungs, and central nervous system, the use of a variety of immunosuppressive treatments--and the recently described 2-chloro-2-deoxyadenosine (2CdA) (cladribine)--have been suggested; however, the type and extent of disease that will respond to this therapy has not yet been clarified. Solid laboratory research and rigorous clinical trials are required for more effective and less toxic therapies for patients with progressive LCH.