Background: Women with atrial fibrillation (AF) may be treated less actively with oral anticoagulation (OAC) than men. Patients and methods: We assessed sex differences in the implementation of stroke risk stratification with CHADS2 and CHA2DS2-VASc scores and reasons not to use OAC in 1747 AF patients suffering their first cerebrovascular event after the AF diagnosis. Results: Women were older and had more often a high stroke risk (CHADS2/CHA2DS2-VASc 2) than men (p < .001). On admission, 46.4% of women and 48.2% of men were on OAC with no sex difference (p ¼ .437). However, of patients without OAC, 74.4% of women and 49.5% of men should have been on OAC based on CHADS2/CHA2DS2-VASc 2 (p < .001). Conversely, 34.8% of men and 17.5% of women on OAC had a low or moderate risk (CHADS2/CHA2DS2-VASc 0–1, p < .001). A valid reason to omit OAC was reported in 38.6% of patients and less often in women (p < .001). Conclusions: OAC was underused in high-risk AF patients, particularly women, but prescribed often in men with low or moderate stroke risk. Reasons for omitting OAC treatment were poorly reported, particularly for women.