OBJECTIVE Patients with interstitial cystitis, a chronic nonbacterial inflammation of the bladder, were investigated for the presence of systemic autoimmune diseases, in particular for Sjögren's syndrome (SS). METHODS Ten patients were included in the study on the basis of a diagnosis of interstitial cystitis according to usual criteria. They underwent clinical and laboratory investigations including those for keratoconjunctivitis (KCS) and focal lymphocytic sialoadenitis (FLS). RESULTS In 2 patients both KCS and FLS were present allowing the diagnosis of primary SS according to classification criteria. Additionally, in 6 patients one of the 2 hallmarks of primary SS was present, KCS in 3 and FLS in 3. CONCLUSIONS Interstitial cystitis is a new example of a disease that occurs in association with SS, supporting the concept that interstitial cystitis is an autoimmune cystitis. The clinical relevance of the finding is that a high index of suspicion for SS is indicated in patients with interstitial cystitis.