Histiocytosis of childhood is characterized by localized or generalized proliferation of cells of the mononuclear phagocyte system and the dendritic cell system. In patients with Langerhans cell histiocytosis, the orbit is the most involved site encountered in ophthalmic practice, usually as a lytic lesion in the zygomaticofrontal suture. Patients usually present with acute or chronic periorbital swelling. Electron microscopic findings of Birbeck granules and positive staining for CD1 antigenic determinant confirm the diagnosis.