A 70-year-old female was diagnosed as having rheumatoid arthritis (RA) in 1971, which was then treated with steroid and nonsteroidal anti-inflammatory drugs. In 1999, after total replacement of her knee joint, 4 mg of methotrexate (MTX) per week was administered. Two months after the MTX administration, 200 mg of bucillamine per day was administered. On May 10, 2001, the patient was rushed to the hospital due to fever and difficulty in breathing. Chest X-ray and computed tomography (CT) revealed shadows of ground-glass-like opacity occurring sporadically in many places in the upper lung field bilaterally and interstitial shadows mainly on the lateral side of the lower lung field bilaterally. Instead of MTX and bucillamine, which were withheld, an MTX antagonist was administered and oxygen-supported therapy was performed; consequently, the patient recovered without the need to increase the amount of steroid. The percentage of lymphocytes in the broncholaveolar lavage fluid increased to 72%, and the CD4/CD8 ratio to 3.13. The level of serum KL-6 increased while that of serum SP-D returned to the normal level at different time. Following MTX and bucillamine administration, shadows of ground-glass-like opacity occurred sporadically in many places in the upper lung field bilaterally, which is not usually observed. It is suggested that such an unusual pulmonary disorder occurred due to concomitant use of drugs or other factors.