Of 3,482,295 people vaccinated with BNT162b2 (Pfizer-BioNTech), 48 developed myopericarditis (HR 1.34 (95% CI 0.90 to 2.00). Adjusted hazard ratios between female participants only and male participants only 3.73. Among 498,814 people vaccinated with mRNA-1273 (Moderna), 21 developed myopericarditis (IR 3.92 (2.30 to 6.68). The risk ratios between women and men were 6.33 ( 2.11 to 18.96) and 3.22 (1.75 to 5.93).Vaccination with mRNA-1273 was associated with a significantly increased risk of myocarditis or myopericarditis in the Danish population, mainly due to an increased risk among people aged 12 to 39 years, while BNT162b2 vaccination was only associated with a significantly increased risk among women.However, the absolute rate of myocarditis or myopericarditis after SARS-CoV-2 mRNA vaccination was low, even in the youngest age groups.