Effectiveness and safety of long-term anticoagulation treatment are uncertain in venous thromboembolism (VTE) patients at intermediate risk of recurrence. We examined the association between treatment beyond 1 year and outcomes in a Danish nationwide register-based study. VTE patients at intermediate risk of recurrence, that is, non-cancer patients with a first-time unprovoked VTE, who started oral anticoagulation treatment within 30 days and were alive 365 days after the index VTE were included and followed between 2007 and 2015. Exposure was extended (>365 days) or intermediate (91–365 days) treatment. Analyses were done using Cox regression on a propensity score weighted population. We included 18 609 patients with 7232 (38.9%) receiving extended treatment. Mean duration of follow-up was 2.6 years. Compared with intermediate treatment, treatment beyond 365 days was associated with a lower weighted risk of recurrent VTE (hazard ratio [HR] 0.56, 95% confidence interval [CI] 0.49–0.65) and all-cause mortality (HR 0.81, 95% CI 0.72–0.90) and an increased risk of major bleeding (HR 1.87, 95% CI 1.58–2.22). In conclusion, extended anticoagulation treatment (predominantly warfarin) beyond 1 year was in real-life settings associated with a lower risk of recurrent VTE and all-cause mortality among VTE patients with an intermediate risk of recurrence. However, an increased bleeding risk should be considered.