Adult-onset Still's disease (AOSD) is a multisystemic inflammatory disorder, but pulmonary involvement is rare. We herein describe the case of a woman diagnosed with AOSD; treatment resolved her symptoms, but nine days later she was admitted with pyrexia and a productive cough. A chest X-ray revealed diffuse pulmonary nodules and patchy shadows. A high-resolution chest computed tomography scan confirmed diffuse infiltration in the pulmonary parenchyma, signs of alveolar nodules, distribution along the lobule center, several areas of tree-in-bud patterns, and bilateral pleural effusion. The patient was treated with high doses of corticosteroids, which rapidly reduced the size of her diffuse pulmonary nodules and dramatically improved her pleural effusion.