BACKGROUND: Incidence and prevalence of atrial fibrillation (AF) is increasing worldwide, and the condition is associated with high risk of adverse clinical outcomes. Increasing global migration results in more diverse patient populations, and knowledge about AF-related outcomes in immigrants is warranted. AIM: To examine clinical outcomes after AF diagnosis across migrant populations in Denmark. METHOD: Patients with first-time AF and sex-, age- and country of origin matched non-AF population (ratio 1:5) were followed from age 45 from 1998 to 2017. Poisson regression was used and stratified by country of origin for the clinical outcomes: stroke, major bleeding, heart failure, and all-cause mortality. Analyses were adjusted for sex, age, comorbidity, contacts to general practitioners, and socioeconomic variables. RESULTS: The population contained 1,940,010 individuals of Danish origin and 47,952 with origin in one of the ten most represented countries. For all outcomes, the adjusted incidence rate ratio (IRR) was higher for individuals diagnosed with AF. For stroke, the lowest and highest IRR were observed for individuals from Pakistan (1.87 [95 %CI: 1.14
3.07]) and Bosnia-Herzegovina (5.32 [95 %CI: 3.37
7.93]), for heart failure: Iraq (5.06 [95 %CI:3.07
8.34]) and Bosnia-Herzegovina (8.10 [95 %CI: 6.07
10.80]), for major bleeding: Finland (2.04 [95 %CI: 1.42
2.95]) and Yugoslavia (3.53 [95 %CI: 2.70
4.62]), and death: Germany (1.60 [95 %CI: 1.51
1.69]) and Pakistan (2.33 [95 %CI: 1.83
2.98]). CONCLUSION: AF was associated with a substantially higher risk of adverse clinical outcomes among Danish-born, and all examined migrant populations. However, the impact of AF appeared to differ according to country of origin, which could indicate potential differences in AF care and compliance.