Background: The IDEAL DVT study showed that it was safe to shorten the duration of elastic compression therapy on an individualised basis after deep vein thrombosis for prevention of post-thrombotic syndrome. In this study, we assessed the cost-effectiveness of this strategy. Methods: IDEAL DVT was a multicentre, randomised, non-inferiority trial that included patients with acute proximal deep vein thrombosis of the leg. After 6 months of elastic compression therapy, patients were randomly assigned (1:1) to the standard 2 years of elastic stocking compression therapy or shortened duration of compression therapy based on the patient's Villalta score. For our cost-effectiveness analysis, we assessed quality-adjusted life-years (QALYs), measured with the three-level version of EQ-5D (EQ-5D-3L; Dutch and UK tariff) and the 36-item Short Form Health Survey (SF-36), and costs in € (health-care and societal perspective) according to the intention-to-treat approach. Data were collected at 3, 6, 12, and 24 months after diagnosis of thrombosis. We calculated incremental net monetary benefit using a QALY threshold of €30 000, and obtained bootstrapped means and 95% CIs. IDEAL DVT is registered with ClinicalTrials.gov, number NCT01429714. Findings: Between March 22, 2011, and July 1, 2015, 865 patients were enrolled in IDEAL DVT. 437 were assigned to individualised duration of elastic compression therapy and 428 to standard duration of elastic compression therapy. Nine patients were eventually excluded because of recurrent venous thromboembolism within 6 months after the first event. From a societal perspective, for every QALY lost measured with the EQ-5D Dutch tariff, cost savings were €305·992 (incremental net monetary benefit €3205, 95% CI 502–5741), and for every QALY lost based on the Short-Form Six-Dimension (SF-6D) utility score (derived from SF-36), cost savings were €6030·941 (€3540, 95% CI 1174–5953). Using the UK tariff for EQ-5D, the individualised strategy was more effective and less costly (€4071, 1452–6647). The probability that the individualised strategy was cost-effective was 99% at a threshold of €30 000 per QALY (EQ-5D Dutch tariff). Interpretation: Individually shortened duration of elastic compression therapy was cost-effective compared with standard duration elastic compression therapy. Use of an individualised approach to elastic stocking compression therapy for the prevention of post-thrombotic syndrome after deep vein thrombosis could lead to substantial costs savings without loss in health-related quality of life. Funding: Netherlands Organisation for Health Research and Development.