OBJECTIVES: /st> To examine in a nationwide cohort whether the risk of myocardial infarction (MI) in patients with rheumatoid arthritis (RA) is comparable to the risk in patients with diabetes mellitus (DM). METHODS: /st> The study included the entire Danish population followed from 1 January 1997 until 31 December 2006. Through individual level-linkage of nationwide administrative registers, the authors identified subjects who developed RA and DM. The risk of MI was analysed using multivariable Poisson regression models including data on cardioprotective drugs, comorbidity and socioeconomic status. RESULTS: /st> From a total of 4 311 022 individuals included in the cohort, 10 477 and 130 215 individuals developed RA and DM respectively. The overall incidence rate ratio (IRR) of MI in RA was 1.7 (95% CI 1.5 to 1.9), which was similar to the risk in DM (1.7 (1.6 to 1.8); p=0.64 for difference). The risk was significantly increased in all groups when stratifying on age and gender, with higher RRs in younger patients. This was especially pronounced in women RA is associated with the same risk of MI as DM, and the risk of MI in RA patients generally corresponded to the risk in non-RA subjects 10 years older.