Diagnosis of rheumatoid arthritis (RA) is mainly based on clinical criteria of symmetric polyarthritis of the hands and feet, with morning stiffness lasting usually more than 1 h. Autoantibodies typical for RA, i.e., rheumatoid factors and anti-cyclic citrullinated peptide, and measurements of inflammation add more specific information, especially for early diagnosis, where clinical presentation may be oligosymptomatic involving only a few joints. These laboratory parameters are also relevant for prognosis of disease persistence, functional impairment and radiological progression.