A 56-year-old woman was initially seen in March 1998 with a complaint of back pain. Her thyroid gland was swollen and the level of TSH was elevated at 10 microU/ml. Chronic thyroiditis with hypothyroidism was diagnosed. Negative reactions were obtained for both anti-thyroglobulin and anti-thyroid peroxidase antibodies. Daily treatment with thyroxine 50 mg was started. A cough developed in August 1998, and her chest radiographs revealed multiple bilateral consolidation shadows. A transbronchial lung biopsy specimen demonstrated mononuclear cells infiltration in the alveolar septa with fibrosis, consistent with nonspecific interstitial pneumonia (NSIP). There were no findings clinically or serologically suggestive of collagen-vascular diseases. Ultimately interstitial pneumonia compatible with the NSIP pattern in association with chronic thyroiditis was diagnosed. Oral prednisolone (30 mg/day) and azathioprine (50 mg/day) administration was initiated. The cough and the shadows on the chest radiographs improved. However, one year after completion of the treatment, interstitial pneumonia recurred. Retreatment with prednisolone and azathioprine has resulted in its improvement.