The aim of this study was to evaluate the 2010 American College of Rheumatology/European League Against Rheumatism (ACR/EULAR) classification criteria for rheumatoid arthritis (RA) in a cohort with early arthritis and true diagnosis confirmed by long-term follow-up. The criteria were tested in the Heinola community-based inception cohort of 121 true RA patients, while the control group consisted of 95 patients with definite spondyloarthritis and swollen joint(s), recruited in the same time. The diagnoses were confirmed by long-term follow-up. The fulfillment of the four 2010 criteria was determined at baseline (arthritis duration less than 6 months). Ninety-five in one hundred twenty-one (79%) of all RA patients, 54/68 (79%) of nonerosive (at baseline) RA patients, and 4/95 (4%) of controls fulfilled the 2010 criteria of RA, with better specificity (96%) than the 1987 ACR criteria (86%) in the same material. At baseline erosions were found in 44% of all RA patients and in 15% of the controls; rheumatoid factor was positive in 87% of the RA patients, but in 1% of the controls. One hundred seven in one hundred twenty-one (88%) of all RA patients and 16/95 (17%) of the controls fulfilled the 2010 total score criteria or were erosive at onset. The 2010 ACR/EULAR criteria should be documented in all patients with arthritis. If the criteria are not fulfilled at baseline in a nonerosive patient, the true diagnose may still be RA due to seroconversion or diagnostic manifestations during the follow-up. Indications for early disease modifying antirheumatic drug treatment may be present in active arthritis also in cases not fulfilling the new criteria at baseline.