A 76-year-old HTLV-I-positive male with acute cerebellar ataxia was suffering from dyspnea on exertion. Chest CT suggested interstitial pneumonitis. Methylprednisolone pulse therapy improved his symptoms and chest CT findings. Twelve months after discharge, when the prednisolone dose was tapered to 5 mg every other day, his lung lesion recurred. The lesion responded initially to steroid therapy. However, hypoxemia intractable to steroid pulse therapy developed and the patient died of respiratory failure. The autopsy revealed diffuse alveolar hemorrhage with no finding of vasculitis. This is the first case report of diffuse alveolar hemorrhage in an HTLV-I carrier.