Objectives: To evaluate the effect of corticosteroid injections in the painful temporomandibular joint (TMJ) of patients with rheumatoid arthritis (RA) in relation to systemic inflammatory activity. Method: Examination of 35 patients (median age 54 years; 89% female) included maximum mouth opening capacity, degree of anterior open bite (AOB), TMJ pain intensity at rest, and crepitus. Serum levels of rheumatoid factor (RF), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), serotonin, and plasma levels of interleukine-1 beta (IL-1 beta) were determined. Out of the 70 examined joints, 53 joints received a corticosteroid (methylprednisolone) injection after the clinical examination at baseline (T0). The examination was repeated for all patients at T1 (median 3.1 weeks after T0), and for 21 patients at T2 (median 6.3 weeks after T1), of whom 20 patients received a second injection at T1. Results: Maximum mouth opening capacity significantly increased, and TMJ pain intensity significantly decreased between T0 and T1, but these improvements were no longer present at T2. No differences were found in AOB between the time points. Of the joints that received an injection at T0, 19 joints had pretreatment crepitus, which resolved in eight joints at T1. No correlations were found between the change in mouth opening capacity or TMJ pain intensity and ESR, CRP, serotonin, or IL-1 beta. Conclusions: Methylprednisolone injections in the TMJ alleviate pain and improve mouth opening capacity for approximately 3 weeks, allowing patients to perform jaw exercises during this timeframe of temporary relief. It thus seems useful for the short-term management of TMJ involvement in RA.