Sinus histiocytosis with massive lymphadenopathy or Rosai-Dorfman disease (RDD) is a rare histiocytic proliferative disorder of unknown etiology. Most patients present with lymph node involvement manifesting as adenopathy; however, RDD may arise primarily in a variety of extranodal sites, including bone. We report herein our experience with 15 cases of primary intraosseous RDD. The patients include 8 females and 7 males, who ranged in age from 3 to 56 (mean 27) years. The lesions arose in a variety of anatomical locations, including the tibia, femur, clavicle, skull, maxilla, calcaneus, phalanx, metacarpal, and sacrum. Radiographically, the lesions were lytic with well defined and usually sclerotic margins. Histologically, the lesions demonstrated the classic features of RDD and consisted of a mixed inflammatory infiltrate with numerous large histiocytes with abundant eosinophilic cytoplasm which exhibited emperipolesis. Some cases also contained numerous neutrophils. Immunohistochemical stains showed that the large histiocytes were S-100 positive. Follow-up information was available for 12 patients. Five patients eventually developed additional extraosseous manifestations, including testicular, lymph node, and subcutaneous lesions. One of these 5 also developed a new bony lesion within the sternum. One patient developed additional lesions within multiple bones of the hand and wrist, without extraosseous disease. One patient had stable bony lesions, whereas 5 remained disease free after treatment.