Bronchiolitis obliterans with organizing pneumonia is a very special disorder. The lesions nearly completely resolve with steroid therapy. Clinical improvement is often dramatic sometimes within two days of the therapy. Because its therapy is so steroid-related, early diagnosis is very important lest the irreversible changes occur. Our patient is a 50 year old man, complaining of cough and progressive dyspnea, that did not respond to antibiotherapy. After our clinical and cytological examinations, we diagnosed him as BOOP. Our diagnosis was supported with the steroid therapy response in the first month.