Chronic glucocorticoids excess leads to morphological and functional cardiac alterations, a substrate for arrhythmias. Autonomous cortisol secretion (ACS) in adrenal incidentalomas is a model of chronic endogenous hypercortisolism.To investigate prevalence and incidence of atrial fibrillation (AF) in a large cohort of patients with ACS.Retrospective study.University Hospital.Patients evaluated between 1990 and 2018 for adrenal incidentalomas (n=632), without pheochromocytoma, primary aldosteronism, Cushing syndrome, congenital adrenal hyperplasia, and adrenal malignancy. Cortisol after 1 mg-dexamethasone suppression test < or >50 nmol/L defined non-secreting tumors (NST) (n=420) and ACS (n=212), respectively.Assessment of AF at baseline (n=632) and during a median follow-up of 7.7 years retrospectively (NST n=249, ACS n=108). Comparison with general population.Prevalence and incidence of AF.AF prevalence was higher in patients with ACS (8.5%) than NST (3.1%, P=0.003) and the general population (1.7%; P<0.001 vs ACS, P=0.034 vs NST). The age-adjusted rate ratio to the general population was 1.0 for NST and 2.6 for ACS. AF was associated with ACS (odds ratio 2.40; 95% confidence interval [CI] 1.07-5.39; P=0.035). The proportion of patients with AF at last evaluation was higher in ACS (20.0%) than NST (11.9%; P=0.026). ACS showed a higher risk of incident AF than NST (HR 2.95; 95%CI 1.27-6.86; P=0.012), which was associated with post-dexamethasone cortisol (HR 1.15; 95%CI 1.07-1.24; P<0.001), independently of known contributing factors.Patients with adrenal incidentalomas and ACS are at risk of AF. ECG monitoring may be recommended during follow-up.