A review of 1,120 cases of histiocytosis X yielded 114 cases with oral involvement. Seventy-eight percent of the oral lesions in this series were categorized as monostotic or polyostotic eosinophilic granuloma. The great majority of cases occurred in males, with 40 percent of the lesions having developed before the patient had reached the age of 10 years. The mandible was involved in 73 percent of the cases, and the posterior jaw region was the predominant site. Extraoral involvement occurred in 70 percent, with the most common sites being the skull and lower extremity. The preferred treatment for oral lesions was surgical curettage, and the prognosis was generally very favorable, as evidenced by the over-all recurrence rate of 16 percent.