A 73-year-old woman was admitted to our hospital because of dyspnea on effort and diffuse ground-glass opacities in bilateral lower lung fields on a chest radiograph. CT scans demonstrated a spiculated nodule measuring 9 mm in diameter in the right S3 and diffuse ground-glass opacities in bilateral lower lobes. Right upper lobectomy and lung biopsy of the right lower lobe were performed using video-assisted thoracoscopic surgery. Histological examination revealed adenocarcinoma in the right S3 and an accumulation of pigmented macrophages in the alveolar spaces of the lower lobe, which was compatible with desquamative interstitial pneumonia (DIP). Five months' cessation of smoking was not sufficiently effective for DIP. Therefore, corticosteroid therapy was started, and resulted in rapid improvement in symptoms, pulmonary function and CT findings had been achieved. It is unlikely that the lung cancer and DIP were closely associated etiologically, because the adenocarcinoma was located far from the area of DIP.