Propylthiouracil (PTU) is a drug used to treat hyperthyroidism. A number of adverse effects have been reported with this drug, including fever, agranulocytosis, skin rash, and vasculitis. PTU-induced interstitial pneumonia is rare--only three cases have been reported--and PTU-induced nonspecific interstitial pneumonia (NSIP) has not been reported. We report a patient who developed NSIP after taking PTU for 1 year. She developed dyspnea, cough, and mild fever lasting 1 month, and a chest CT scan showed multifocal patchy consolidation in both lungs. She underwent a surgical lung biopsy, and NSIP was confirmed pathologically. The symptoms and abnormalities seen in the chest radiograph improved after withdrawal of PTU. To our knowledge, this is the first documented case of pathologically proven PTU-induced NSIP.