Adenovirus pneumonia is uncommon but its severe infection has a mortality as high as 10%, and survivors may have residual airway damages, manifested by bronchiectasis, bronchiolitis obliterans, or pulmonary fibrosis. We report a case of adenovirus pneumonia demonstrating fatal respiratory distress. Adenovirus was isolated from pharyngeal specimens using cell culture and typed as serotype 3 by a combination of polymerase chain reaction (PCR) and restriction fragment length polymorphism analysis. The patient characteristically showed hypercytokinemia, characterized by increased levels of lactate dehydrogenase, ferritin, and several cytokines including interferon-γ and interleukin-6. We treated the patient with pulse methylprednisolne therapy (25 mg/kg/day, for 3 days), resulting in the rapid amelioration of respiratory distress. This is the first report describing the treatment of pulse methylprednisolone therapy in fatal adenovirus pneumonia. During the clinical course, serum Krebs von den Lungen-6 (KL-6), which is a marker for the activity of diffuse interstitial lung disease, was elevated, suggesting that serum KL-6 could be available as a marker of pulmonary prognosis in viral pneumonia.