Diffuse dendriform pulmonary ossification is a rare disorder characterized by widespread pulmonary ossification distributed in a characteristic branching pattern. It is usually associated with chronic interstitial inflammation and fibrosis but may occasionally be idiopathic. The underlying pathogenesis remains uncertain. Computed tomography findings characteristically show fine branching heterotopic bone formation within the lungs, often in a lower lobe distribution. A case of idiopathic dendriform ossification is described in a 34-year-old man who presented for investigation of hemoptysis.