Anti-cyclic citrullinated peptide antibody (anti-CCP antibody) is very useful for the diagnosis of rheumatoid arthritis (RA) and is associated with articular erosions. The specificity of anti-CCP antibody in the diagnosis of RA has been reported to be about 95 %. Because of its higher specificity in RA, we assessed the clinical features of primary Sjogren's syndrome (pSS) who were positive for anti-CCP antibody. We assessed the clinical features of 405 pSS patients. After 60 (range 7-98) months, 23 (5.6 %) patients previously diagnosed with pSS had progressed to RA. Comparing the anti-CCP positive group with the negative group, laboratory test results for anti-CCP titer and rheumatoid factor positivity with respect to clinical outcome and progression to RA, arthralgia and arthritis were significantly different. Multivariate regression analysis also showed that anti-CCP antibody titer was independently associated with progression to RA. The odds ratio of anti-CCP positivity in terms of progression to RA was 2.5 (95 % CI 1.7-3.7). Testing for anti-CCP antibody in pSS patients with arthritis may allow for the prediction of progression to RA.