Objectives To investigate geographical variation in initiation and extended treatment with anticoagulants and clinical outcomes among patients hospitalized with first-time venous thromboembolism (VTE) in Denmark between 2007 and 2018. Methods Using nationwide health care registries, we identified all patients with a first-time VTE hospital diagnosis supported by imaging data from 2007 to 2018. Patients were grouped according to residential region (5) and municipality (98) at the time of VTE diagnosis. Cumulative incidence of initiation of and extended (beyond 365 days) anticoagulation treatment as well as clinical outcomes, including recurrent VTE, major bleeding, and all-cause death, were assessed. Sex- and age-adjusted relative risks (RRs) of the outcomes were computed when comparing across individual regions and municipalities. Overall geographic variation was quantified by computing the median RR. Results We identified 66,840 patients with a first-time VTE hospitalization. A difference in initiation of anticoagulation treatment of more than 20 percentage points between regions was observed (range: 51.9–72.4%, median RR: 1.09, 95% confidence interval [CI]: 1.04–1.13). Variation was also observed for extended treatment (range: 34.2–46.9%, median RR: 1.08, 95% CI: 1.02–1.14). The cumulative incidence of recurrent VTE ranged from 3.6 to 5.3% at 1 year (median RR: 1.08, 95% CI: 1.01–1.15). The difference remained after 5 years, and variation was also observed for major bleeding (median RR: 1.09, 95% CI: 1.03–1.15), whereas it appeared smaller for all-cause mortality (median RR: 1.03, 95% CI: 1.01–1.05). Conclusion Substantial geographical variation in anticoagulation treatment and clinical outcomes occurs in Denmark. These findings indicate a need for initiatives to ensure uniform high-quality care for all VTE patients.