Background Atrial fibrillation is associated with increased cardiovascular morbidity and mortality. Hypertension is an important risk factor for the development of atrial fibrillation. Aim This study assessed the relationship between blood pressure control and new-onset atrial fibrillation in hypertensive patients. Methods and results We followed 45,530 hypertensive patients with no previously documented atrial fibrillation, attending primary healthcare in Sweden during 2001-2008. After a mean follow-up of 3.5 years 2057 patients (4.5%) developed atrial fibrillation. Compared to patients with no atrial fibrillation, the new-onset atrial fibrillation group (after adjustment for age, sex, diabetes mellitus, heart failure, ischaemic heart disease, cerebrovascular disease and number of visits) had higher mean in-treatment systolic blood pressure (SBP) and diastolic blood pressure of 3.8?mmHg (95% confidence interval (CI) 3.0-4.6; P?