A 29-year-old man presented with a four-week history of pneumonic symptoms and progressive roentenographic infiltrates which were unresponsive to orally administered antibiotics. Bronchoscopy failed to identify an infectious etiology, but abundant atypical lymphocytes in the bronchial washings were present. A diagnosis of adult T-cell leukemia/lymphoma was subsequently made. After administration of cancer chemotherapy, the pneumonic symptoms and chest roentgenogram infiltrates resolved. This report suggests that ATL can present as an acute noninfectious pneumonitis.