A case of a 64-year-old woman who had undergone resection of a femoral giant cell tumor in another hospital 35 years before was referred to our hospital for diabetes education. Chest radiography and computed tomography (CT) revealed diffuse densely calcified nodular lesions that appear to be in both lung fields. Since pulmonary metastases of the giant cell tumor of the bone was suspected, she underwent a lung biopsy, which showed diffuse pulmonary ossification (DPO) of the dendriform type. It is extremely rare that idiopathic DPO is diagnosed by lung biopsy.