In this Dutch multicentre superiority trial, patients with a first-time acute iliofemoral deep-vein thrombosis (DVT) were randomized in a 1:1 fashion to standard treatment (systemic anticoagulation and compression stockings) plus ultrasound-accelerated catheter-directed thrombolysis with the Ekos Endowave® system (EKOS Corporation, Bothell, WA, USA) combined with urokinase as thrombolytic agent or to standard treatment only. The primary endpoint was the diagnosis of the postthrombotic syndrome, which was defined as a Villalta score of ≥5 (on two occasions at least 3 months apart) at 12 months after the acute event. Secondary endpoints included health-related quality of life, recurrence of venous thromboembolism, pulmonary embolism, in-stent thrombosis and death. Between 2010 and 2017, 184 patients were randomized. The rate of the diagnosis of the postthrombotic syndrome, which was the primary outcome parameter, was 29% in the interventional treatment arm and 35% in the standard treatment arm (p=0.42). Regarding secondary outcomes, recurrent (non-stent) DVT occurred in 5 patients of the interventional treatment arm and 4 patients of the conservative treatment arm. Stent-thrombosis was observed in 10 patients of the interventional treatment arm. Pulmonary embolism occurred in no interventionally treated patient, but in 2 conservatively treated patients. One interventionally treated patient died, while 3 conservatively treated patients died during the follow-up period. Four patients of the interventional treatment arm suffered from major bleeding (no patients of the conservative treatment arm). Changes in healthy-related quality of life measures between baseline and 12 months were similar between both treatment arms.