Langerhans histiocytosis is a rare multi-systemic disease defined by the accumulation of Langerhans cells in the various organs of the human body, it predominates in children. Different localizations are described, Including the hematological localization characterized by the presence of histiocytes cell in the bone marrow. The aim of this work is to show the interest of the medullogram in the diagnosis of histiocytosis. We report 3 cases of Multifocal langerhanstic histiocytosis diagnosed in the hematology department in the Hassan II University Hospital in Fez. The diagnosis of Langerhans' histiocytosis was retained on clinical, cytological and anatomopathological criteria.