A case of renal adenocarcinoma in the ossifying kidney is presented. The patient was a 22-year-old woman, who had been diagnosed as having renal teratoma in her right renal tumor with calcification on the basis of the urological examinations including retroperitoneal pneumography and abdominal aortography one and a half years prior to the time when she was incidentally found to have osteolytic lesion in the left clavicle on chest plain film. Further roentgenographic examinations revealed multiple osteolytic lesions of the bones, a right kidney tumor with multilocular cyst-like calcified shadow and neovaacularity.Right nephrectomy was performed under the preoperative diagnosis of right renal malignancy with multiple bone metastases.Grossly, multicystic lesion with irregular surface and stony hard consistence was found not inside but beside the tumor.Microscopically, bone formation was found within the wall of the calcified cysts without tumor cells, but with tumor invasion. Sections of the tumor showed both adenomatous adenocarcinoma and dark cell type of adenocarcinoma.Five cases of ossifying renal adenocarcinoma have been reported in Japan, but this is probably the first case of adenocarcinoma in the ossifying kidney.