Sjögren's syndrome (Sjs) can cause many organic changes, but is rarely accompanied by pleuritis. We report here a 62-year-old patient with subclinical Sjs who developed unilateral pleuritis with moderate effusion. He was diagnosed to have subclinical Sjs based on the positivity of anti SS-A/SS-B antibodies and the biopsy findings of minor salivary glands which revealed lymphocyte infiltration around the duct. In the pleural effusion, both increased lymphocytes and anti SS-A/SS-B antibodies were observed. He showed no signs of infection nor malignancy. There was no direct evidence that he had other collagen diseases which cause pleuritis. We conclude that the pleuritis was caused by Sjs. In patients with Sjs, activated polyclonal B lymphocytes and autoantibodies are considered to cause systemic tissue damage. This case indicates that these factors can cause pleuritis in Sjs patients.