ABSTRACT
Histiocytosis is a term applied to a group of rare disorders of the reticuloendothelial system. Langerhan cell histiocytosis (LCH) is characterized by the clonal proliferation of a special type of cell, the Langerhans cell. These are dendritic antigen-presenting cells that are normally distributed in many organs. LCH is presents as one of three clinicopathologic entities: acute disseminated Langerhan cell histiocytosis (Letterer- Siwe syndrome), unifocal eosinophilic granuloma, or multifocal eosinophilic granuloma. Unifocal lesions usually affect the skeletal system and may be asymptomatic, may cause pain and tenderness and in some instances, pathological fractures. This disorder is relatively indolent and may regress spontaneously or needs local excision or irradiation. We present a case of solitary eosinophilic granuloma of frontal bone.