A 56-year-old woman was admitted to the hospital because of dry coughing and shortness of breath on exertion. In addition, dry eyes and cornea guttata suggested Sjögren's syndrome. Chest radiography revealed linear, reticular shadows throughout the lung fields, and enlargement of hilar and mediastinal lymph nodes. A specimen was obtained by transbronchial lung biopsy but the findings were not condusive; open-lung biopsy was done. The histopathological findings suggested lymphocytic meterstitial pneumonia. Results of genetic analysis and of immuno-histochemical examination conformed that the proliferating lymphocytes were polyclonal. Corticosteroids and immunosuppressive drugs have been used to treat lymphocytic interstitial pneumonia, and they were effective in this case.