OBJECTIVE: The 2010 New American College of Rheumatology/European League Against Rheumatism (ACR/EULAR) criteria for rheumatoid arthritis (RA) was raised to identify patients with early RA and replaced the 1987 ACR classification criteria. The aims of this study are to assess the availability of new classification criteria and to evaluate its potential limitation. METHODS: A total of 408 patients with newly diagnosed RA were included from 13 secondary or tertiary hospitals in South Korea. The symptom duration was less than 12 months before the diagnosis of RA. RA was defined as either 1987 ACR classification criteria or new 2010 ACR/EULAR criteria. We compared the full details of both classification criteria. RESULTS: The mean symptom duration was 5.1 months. The majority (76.2%) of the patients were female. Two hundred and seventy three patients (66.9%) fulfilled both of the 2010 and 1987 classification criteria. Forty-seven (14.7%) of the 320 patients fulfilling the 1987 criteria did not fulfill the new classification criteria. On the other hand, eighty-eight (24.4%) of the 361 patients fulfilling the 2010 ACR/EULAR classification criteria did not fulfill the 1987 ACR criteria. Thirty-six (55.4%) of the 65 patient with seronegative RA failed to meet the 2010 classification criteria. In case of seropositive RA (n=343), 85 additional patients (24.8%) could be diagnosed as RA using new classification criteria. CONCLUSION: The new 2010 ACR/EULAR classification criteria enable physicians to diagnose more patients with early RA via the help of serology. However, the sensitivity for the diagnosis of seronegative RA is projected to decrease.