Langerhans cell histiocytosis (ex histiocytosis X) is usually present in children. It is a clonal proliferation of non-functional Langerhans's cells. Histological aspects are variable. The diagnosis is made in immunolabeling by anti-CD1a. Clinical presentations are variable, depending on their extension. Three syndromes are actually the same pathogenic process: eosinophilic granuloma (single or multiple osseous localizations), Hand-Schüller-Christian disease (chronic form with bone and visceral dissemination) and Abt-Letterer-Siwe disease (disseminated and acute malignant presentation).