BACKGROUND: Several studies have shown that the prescription of antiplatelet therapy (APT) is associated with an increased risk of oral anticoagulant (OAC) underuse in patients aged 75 years and over with atrial fibrillation (AF). An associated atheromatous disease may be the underlying reason for APT prescription. The objective of the study was to determine whether the association between underuse of OAC and APT prescription was explained by the presence of an atheromatous disease. METHODS AND RESULTS: We performed a retrospective, observational, single-centre study between 2009 and 2013 based on administrative data. Patients aged 75 years and over with non-valvular AF were identified in a database of 72,090 hospital stays. Prescriptions of anti-thrombotic medications and their association with the presence of atheromatous disease were evaluated by the mean of a logistic regression. A total of 2034 hospital stays were included (mean age 84.3 ± 5.2 years). The overall prevalence of known atheromatous disease was 25.9%. OAC underuse was observed in 58.5% of the stays. In multivariable analysis, the prescription of an APT was associated with an increased risk of OAC underuse [odds ratio (OR) 6.85; 95% confidence interval (CI) 5.50-8.58], independently of the presence of a concomitant known atheromatous disease (OR 0.78; 95% CI 0.60-1.01). Among the 692 stays with APT monotherapy (34.0%), 232 (33.5%) displayed an atheromatous disease. CONCLUSIONS: The underuse of OAC is associated with the prescription of APT in older patients with AF, regardless of the presence or absence of known atheromatous disease. Our results suggest that APT is often inappropriately prescribed instead of OAC.