The widespread clinical use of hemodialysis has prolonged the survival of a vast number of uremic patients, but it has also yielded some problems including renal osteodystrophy. Recently, it has become well known that the clinical use of active vitamin D metabolites is effective in many patients with renal osteodystrophy. However, there are many patients with bone diseases resistant to such treatment. Several lines of evidences implicate aluminum as one of the causal factors in the production of such diseases. We recently found 20 patients with bone diseases associated with the deposition of aluminum in front of active calcification in the bone. All of them were undergoing maintenance hemodialysis with softened water thrice weekly and taking aluminum containing antacids and 1 alpha-(OH)D3. The age of the patients ranged between 30 y.o. and 62 y.o. (46.5 +/- 9.0, mean +/- s.d.). All of them had severe bone pain and 8 of them had bone fractures. Bone X-ray, bone scintigraphy, serum Ca, P, ALP, serum aluminum and bone histology were examined. Based on the bone histology, they were classified into four types; inactive type (9), osteomalacia type (6), mild type (4) and mixed type (1). There were no significant differences among each group concerning serum values of Ca, P and aluminum. Serum value of ALP tended to be high in the osteomalacia type, and that of c-PTH was significantly low in the inactive type compared with the other types. Our finding suggest that aluminum associated bone disease is not so rare in Japan and show that the diagnosis of this disease should be made histologically and that clinical and blood chemical features are not reliable for the diagnosis of aluminum associated bone disease in hemodialysis patients.