A 53-year-old woman who had xerostomia for ten years was admitted to our hospital because of refractory lower abdominal pain and pollakisuria of five years duration. Although she had undergone surgical treatments including cholecystectomy, ovarian cystectomy and groin hemiorrhaphy, she still suffered from abdominal symptoms. A diagnosis of interstitial cystitis was confirmed by hydraulic distention during a cystoscopic examination and by histopathological examination of the bladder. Her symptoms disappeared soon after the cystoscopic procedure, which also had a therapeutic effect of interstitial cystitis. Laboratory findings revealed hypergammaglobulinemia, a high titer of rheumatoid factor, positive anti-nuclear antibody, and positive anti-SS-A/Ro antibody. She was diagnosed as having primary Sjögren's syndrome based on the results of a gum test (8.5 ml/ 10 min), sialography (Stage II), and a positive minor salivary gland biopsy. Starting one month after the hydraulic distention, her abdominal symptoms gradually reappeared along with elevation of her serum IgG level. These features were markedly improved with 30 mg/day of oral prednisolone, which was then successfully tapered. These results suggested that interstitial cystitis in this case was caused by immunological abnormalities associated with Sjögren's syndrome.