Acute mercury inhalation poisoning is a rare cause of acute lung injury. It is usually fatal because of progressive pulmonary failure. We experienced a patient with acute respiratory distress syndrome (ARDS) after illicit use of mercury vapor for hemorrhoid treatment; he developed acute chemical pneumonitis following exposure to mercury vapor. Prompt treatment with corticosteroids and penicillamine for acute chemical pneumonitis was instituted; radiologic pulmonary infiltrates disappeared within a week, but late phase neurologic sequelae and pulmonary interstitial fibrosis progressed.