A 26-year-old man presented at our hospital in 2008 to undergo detailed investigations as part of a routine health examination. Chest computed tomography (CT) showed linear and reticular opacities with, in part, diffuse calcification in the lung fields bilaterally. A surgical lung biopsy was performed and the histological findings were compatible with a diagnosis of diffuse pulmonary ossification (DPO) of the dendriform type. DPO usually occurs as a secondary disease. As the histological changes in interstitial fibrosis were minimal rather than diffuse and not significant enough to be regarded as interstitial pneumonia, we considered this to be an idiopathic case. However, the findings appear to suggest that inflammation and fibrosis were associated with ossification.