61 cases of histiocytosis X of jaws were reported here. They occurred more often in man (72% of men) than in woman, with an average age of 27 years. The mandible was affected more frequently than the maxilla. Clinically, dental expulsion, gingival swelling, fractures or pain were the usual symptoms. Roentgenographic examination showed either central or peripheral (alveolar bone) osteolytic areas. The histologic diagnosis was easy when eosinophilic polymorphous leukocytes or histiocytes were preponderant. In the other cases, immunohistochemistry (positivity of S-100 protein) and electron microscopy (presence of Birbeck granules about paraffin embedded specimens) were of a great usefulness. The prognosis of the disease was mainly related to the diffusion of lesions to other skeletal portions or extraskeletal localizations (37% of our cases). It has been improved by combination of chemotherapy to surgery (despite of frequent recurrences), 40 upon 45 patients are well after a follow-up of 2 to 10 years after the last localization.