We describe the first case, to our knowledge, of usual interstitial pneumonia (UIP) as the pulmonary manifestation in primary Sjögren's syndrome (SjS). A 45-year-old woman was admitted to our hospital because of a dry cough and an interstitial shadow on a chest roentgenogram. Labial biopsy and sialogram confirmed a diagnosis of SjS. BAL fluid analysis revealed lymphocytosis with a decreased CD4/CD8 ratio compatible with bronchiolitis obliterans organizing pneumonia or lymphoid interstitial pneumonia. Open-lung biopsy specimen, however, showed evidence of UIP. Open-lung biopsy was a useful and necessary examination to determine the nature of the pulmonary complication in primary SjS. Conservative treatment without corticosteroids maintained a stable condition for a follow-up period of 3 years.