A 44-year-old woman was admitted to our hospital complaining of dyspnea. A chest X-ray film obtained on admission showed bilaterally shrunken lungs, and peripheral bundle-like and linear shadows. A chest CT scan revealed marked thickening of bronchovascular bundles and low lung volumes. Mild dryness of the mouth, and the results of a Rose-Bengal test, Schirmer test, and sialography led to the diagnosis of primary Sjögren's syndrome. Corticosteroid pulse therapy was followed by slight improvement. To determine the pathological diagnosis and to plan further therapy, video-assisted thoracoscopic lung biopsy was done. Examination of the biopsy specimen revealed alveolitis and infiltration of lymphocytes, which suggested active interstitial pneumonia. Therapy with corticosteroids and the immunosuppressant azathioprine was followed by marked improvement.