Abstract Aims To investigate if patients with atrial fibrillation (AF) without clear indication for oral anticoagulant (OAC) due to perceived low stroke risk may benefit from OAC treatment when also dementia and intracerebral bleeding risks are considered. Methods and results Retrospective study of cross-matched national registries of all individuals in Sweden with a hospital diagnosis of AF between 2006 and 2014 (n = 456 960). Exclusion was made of patients with a baseline CHA2DS2-VASc score >1, not counting female sex, and of patients with previous diagnosis of dementia or intracranial bleeding. After exclusions, 91 254 patients remained in the study of whom 43% used OAC at baseline. Propensity score matching and falsification endpoints were used. Treatment with OAC was associated with lower risk of dementia after adjustment for death as a competing risk [subhazard ratio (sHR) 0.62 with 95% confidence interval (CI) 0.48–0.81]. Regarding the composite brain protection endpoint, OAC treatment was associated with an overall 12% lower risk (sHR 0.88, CI 0.72–1.00). This apparent benefit was restricted to patients aged >65 years, whereas OAC treatment of patients <60 years of age without risk factors appeared to do more harm than good. Conclusion Low-risk AF patients who take OAC have lower risk of dementia than those who do not use OAC. Patients age >65 years appear to benefit from OAC treatment irrespective of stroke risk score.