OBJECTIVE: Patients with rheumatoid arthritis (RA) who also have diabetes mellitus (DM) might have worse clinical outcomes and adverse events compared to patients with RA who do not have DM. We evaluated the effects of DM on Health Assessment Questionnaire (HAQ) changes and outpatient infection rates in patients with RA. METHODS: Using the American College of Rheumatology's Rheumatology Informatics System for Effectiveness (RISE) electronic health record-based registry, we identified patients with RA who had ≥ 1 rheumatologist visit with a HAQ measured in 2016 (index visit), ≥ 1 previous visit, and a subsequent outcome visit with the same HAQ measured at 12 months (± 3 months). We identified DM by diagnosis codes, medications, or laboratory values. Outpatient infection was defined by diagnosis codes or antiinfective medications. We calculated mean HAQ change and incidence rate (IR) of outpatient infections among patients with and without DM. Generalized linear models and Cox regression were used to calculate the adjusted mean HAQ change and HRs. RESULTS: We identified 3853 RA patients with DM and 18,487 without DM. The mean HAQ change between index and outcome visit among patients with DM was 0.03 and without DM was 0.002 (P < 0.01). We identified 761 outpatient infections for patients with DM with an IR of 22.6 (95% CI 21.0-24.2) per 100 person-years and 3239 among patients without DM with an IR of 19.8 (95% CI 19.1-20.5). The adjusted HR of outpatient infections among patients with DM was 0.99 (95% CI 0.91-1.07), compared to patients without DM. CONCLUSION: Patients with RA with concomitant DM had greater worsening, or less improvement, in their functional status, suggesting additional interventions may be needed for RA patients with DM to optimize treatment and management of other comorbidities.