The use of anti-CCP antibodies has been included in the classification criteria of RA developed by the American College of Rheumatology (ACR) in 2010 and generated the presence of two sub-groups of patients with RA, the positive and negative for anti-CCP. It is very important to study the presence of anti-CCP antibodies in RA population because it influences the clinical behavior and response to treatment. In very early or undifferentiated arthritis, the presence of anti-CCP antibodies can predict the presence of erosions in the course of the disease. On the other hand, patients with negative anti-CCP antibodies tend to have better responses to treatment with methotrexate.