We report a case of slow-resolving pneumonia secondary to bronchiolitis obliterans organizing pneumonia (BOOP) in a 73-year-old woman. Owing to a delayed diagnosis of BOOP, the clinical course was quite long. This syndrome is caused by a nonspecific inflammatory pneumonitis, either idiopathic or associated with infectious or irritant agents (or drugs). It generally presents as a flu-like illness, followed by progressive dyspnea, cough, fever, and bilateral patchy alveolar infiltrates, and lasts several weeks. The diagnostic work-up of slow-resolving pneumonia is discussed.