Diffuse pulmonary ossification (DPO) is an uncommon condition that is characterized by metaplastic bone formation in the lung parenchyma. It is usually not diagnosed clinically and may be apparent radiographically only when extensive. However, it is occasionally encountered at autopsy or on pathologic evaluation of surgical specimens. This article will review the clinical, histologic, and radiographic manifestations of DPO, focusing primarily on the chest radiograph and CT findings, both of which may be underappreciated, for even experienced radiologists may confuse DPO with other entities such as metastatic calcification as seen in chronic renal failure or chronic granulomatous disease.