OBJECTIVE To identify tools designed to evaluate the severity of patients with rheumatoid arthritis (RA) in order to use them in the investigation of prognostic markers in early arthritis. METHODS We conducted a systematic review of studies that developed/validated an index for RA disease severity. They were analyzed using the COSMIN checklist to assess their methodological quality. In addition, all the variables included were evaluated for their clarity of definition, feasibility and probability of being present in each outcome during the first 2 years of the disease course. To estimate redundancy, variables were grouped by domains. RESULTS After reviewing 3,519 articles, 3 studies were included. The first study, the PAS, assessed whether current and lifetime treatment with disease-modifying antirheumatic drugs and/or biologics accurately predicted RA severity, as measured by the patient-reported PAS. Treatment variables did not fully distinguish patients in the highest and lowest quartiles of PAS scores. Another severity index, the Claims-Based Index for RA Severity (CIRAS), included the variables age, sex, Felty's syndrome, number of rehabilitation and rheumatology visits, test for inflammatory markers, number of chemistry panels/platelet counts ordered and rheumatoid factor test. The correlation was low (r=0.56) with an index previously validated by the same research group, the RA medical records-based index of severity (RARBIS), with Disease Activity Score-C-reactive protein (DAS28-PCR) (r=0.07) and Multidimensional Health Assessment Questionnaire (MD-HAQ) (r=0.008). Finally, the RARBIS, used to validate the CIRAS, was devised as an RA severity index based on medical records. It includes as domains surgery, radiology, extra-articular manifestations, clinical and laboratory variables, previously chosen by an expert panel. RARBIS had a weak correlation with treatment intensity (r=0.35) and with DAS28 (r=0.41). CONCLUSIONS There is no index to assess the severity of RA based on the course of the first 2 years of follow-up that is adapted to the current strategy of therapeutic management of this disease. Therefore, we believe it is reasonable to develop a new ad hoc severity index for patients with early arthritis.