OBJECTIVE: To evaluate disease flare and post-vaccination reactions (reactogenicity) in patients with rheumatic and musculoskeletal diseases (RMD) following two-dose SARS-CoV-2 mRNA vaccination. METHODS: 1377 patients with RMD who received two-dose SARS-CoV-2-mRNA vaccination between 16 December 2020 and April 15, 2021 completed questionnaires detailing local and systemic reactions experienced within 7 days of each vaccine dose (D1, D2), and one month after D2 detailing flare of RMD. Associations between demographic/clinical characteristics and flare requiring treatment were evaluated using modified Poisson regression. RESULTS: 11 percent reported flare requiring treatment; there were no reports of severe flares. Flare was associated with prior SARS-CoV-2 infection (IRR 2.09, p=0.02), flare in the six months preceding vaccination (IRR 2.36, p<0.001) and use of combination immunomodulatory therapy (IRR 1.95, p<0.001). The most frequently reported local and systemic reactions included injection site pain (D1 87%, D2 86%) and fatigue (D1 60%, D2 80%); reactogenicity increased after D2, particularly for systemic reactions. No allergic reactions or SARS-CoV-2 diagnoses were reported. CONCLUSION: Flare of underlying RMD following SARS-CoV-2 vaccination was uncommon. There were no reports of severe flare. Local and systemic reactions typically did not interfere with daily activity. These early safety data can help address vaccine hesitancy in patients with RMD.