Rheumatoid arthritis (RA) is a common systemic autoimmune disease with a prevalence of about 1% worldwide . The American College of Rheumatology (ACR) criteria for the classification of RA  are not very well suited to diagnose RA at an early stage of the disease [3, 4], because these criteria rely heavily on the expression of clinical symptoms of RA. In early RA these clinical parameters are often not (yet) manifest. Therefore, a specific and sensitive (serological) marker, which is present very early in the disease, is needed. A good marker should ideally not only indicate the development of the disease, but also be able to predict its erosive or non-erosive progression. The serological parameter that meets these requirements for a good and useful marker for early RA is the anti-citrullinated protein antibody. The sensitivity of this antibody is comparable to that of the rheumatoid factor (RF) (approximately 80%), but its specificity is much higher, about 98%. Several assays have been developed to detect this class of autoantibodies, which are termed anti-CCP because the most sensitive test is based upon cyclic citrullinated peptides. This review will discuss the potential of this autoantibody system for the diagnosis and prognosis of RA.