A retrospective analysis of concurrent bone scintigraphs of 30 patients with histologically confirmed histiocytosis X was carried out to assess the pattern and distribution of bone lesion and the sensitivity of bone scintigraphy with reference to skeletal radiography. Totals of 41 regional and over 90 numeric bone lesions were found in all patients. Single bone lesions were seen in 15 patients and multiple lesions in 12 patients. Three patients had not revealed bone lesion. Distribution of lesions was skull, vertebrae, femur, ribs, mandible and thelike, in the order of decreasing frequency. Unlike previous citations, the sensitivity of bone scan was relativelyas high as over 85% and it showed tow lesions of skull and clavicle which escaped from radiologic detection. Improvement of mechanical resolution and bone-seeking radiopharmaceuticals made it possible to detect bone lesionsin histiocytosis X more accurately than previous decade. Bone scintigraphy could be the effective, helpful diagnostic procedure in the initial diagnosis as well as convenient follow-up method in histiocytosis X.