AbstractAimTo study association between country of birth and risk of first-onset atrial fibrillation (AF) in first- and second-generation immigrants to Sweden under 45 y of age.MethodsThe study population included all individuals (n = 3 248 457) under the age of 45 y in Sweden, including immigrants (n = 722 249). AF was defined as first registered diagnosis in the National Patient Register. Association between country of birth and risk of AF was assessed by Cox regression, calculating HRs and 95% CIs, using Swedish-born individuals as referents. All models were stratified by sex, and in different models were adjusted for age, area of residence in Sweden, educational level, marital status, neighbourhood socioeconomic status and co-morbidity(ies).ResultsA higher fully adjusted HR of incident AF was found in the total sample of first-generation immigrants, 1.44 (95% CI 1.35 to 1.54), in males born in Denmark, Lebanon and Iraq, and in females born in Turkey and Iraq. Lower HRs were found in male and female immigrants from Latin America and Iran, and female immigrants from Finland. Among second-generation immigrants, the fully adjusted HR was significantly lower, 0.70 (95% CI 0.58 to 0.83).ConclusionsClinicians may show a greater awareness of AF in some groups of younger immigrants to enable early diagnosis.