Patients undergoing treatment for acute lymphoblastic leukemia (ALL) are at risk for thrombosis, in part due to the use of L-asparaginase (L-ASP). Antithrombin (AT) replacement has been suggested to prevent VTE and thus might increase exposure to ASP. We report herein the results of the prophylactic replacement strategy in the pediatric-inspired prospective GRAALL-2005 study. Between 2006 and 2014, 784 adult patients with newly diagnosed Philadelphia-negative ALL were included. The incidence rate of VTE was 16% with 69% of them occurring during induction therapy. Most patients received AT supplementation (87%). After excluding patients who did not receive L-ASP or developed thrombosis before L-ASP, AT supplementation did not have a significant impact on VTE (8% versus 14%, OR: 0.6, p=0.1). Fibrinogen concentrates administration was associated with an increased risk of VTE (17% versus 9%, OR 2.2, p=0.02) whereas transfusion of fresh-frozen plasma had no effect. Heparin prophylaxis was associated with an increased risk of VTE (13% versus 7%, OR 1.9, p=0.04). Prophylactic measures were not associated with an increased risk of grade 3-4 bleeding complications. The rate of VTE recurrence after L-ASP reintroduction was 3% (1/34). In ALL patients receiving L-ASP therapy, the use of fibrinogen concentrates may increase the risk of thrombosis and should be restricted to rare patients with hypofibrinogenemia-induced hemorrhage. Patients developed VTE despite extensive AT supplementation which advocates for additional prophylactic measures. While this large descriptive study was not powered to demonstrate the efficacy of these prophylactic measures, it provides important insight to guide future trial design. NCT00327678.