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To estimate the nationwide incidence of rheumatoid arthritis (RA) in Sweden, including its variation across age, sex, geography, and demography, and to describe the sensitivity of register‐based incidence estimates to different RA case definitions.

Incident RA patients were identified using the Swedish National Patient Register. In the base case, incident RA was defined as first‐ever inpatient or nonprimary outpatient care visit listing an RA diagnosis in 2006–2008, with a second visit listing RA within 1 year. Patients prescribed disease‐modifying antirheumatic drugs more than 6 months prior to the first visit listing RA were not regarded as incident. The robustness of this definition was evaluated by more liberal and strict criteria, and by penetration of antirheumatic treatment.

Between 2006 and 2008, 8,826 individuals were identified as incident RA patients. The overall incidence was 41 …