We describe here the first known case in Korea of pulmonary involvement with peripheral T cell lymphoma and the patient presented with severe hypoxic respiratory failure. A 57-yr-old man was admitted to our hospital with rapid progression of dyspnea and bilateral diffuse infiltration on a chest radiograph. He received mechanical ventilation and low dose corticosteroid treatment under the suspicion of critical illness-related corticosteroid insufficiency. Transbronchial lung biopsy revealed large atypical lymphoid cells with positivity for CD3+. We diagnosed this patient as having a peripheral T cell lymphoma and we treated him with high dose corticosteroid. His clinical and radiologic findings rapidly improved and then he received a full dose of chemotherapy for the peripheral T cell lymphoma.