This is a rare case of Dyskeratosis Congenita (DC) with acute interstitial pneumonia. A 51-year-old man with DC was admitted to our hospital because of cough, sputum and fever. Chest X-ray film showed ground glass opacities in all lung fields for a while steroid's therapy proved effective, but about seven months later the patient's condition became serious. Methylprednisolone, cyclophosphamide and mechanical ventilation therapy were not effective. He died and an autopsy was performed. The lung specimen showed Organizing Diffuse Alveolar Damage, and some parts pointed to bacterial infection. But Pneumocystic carinii pneumonia and Fungal infections were not found. It is therefore necessary to conduct intensive examinations of lung involvement of patients with Dyskeratosis Congenita.