Background: The prognosis of adult patients with acute lymphoblastic leukemia (ALL) has improved with the adoption of pediatric-inspired chemotherapy regimens. PEGylated asparaginase (PEG-Asp) is essential to these regimens. Although PEG-Asp is associated with an increased risk of coagulopathy, venous thromboembolism, and depletion of antithrombin III (AT3), there is limited data evaluating the risk of thrombosis and bleeding and optimal antithrombotic interventions in these patients are unknown. Methods: We performed a single-center retrospective study of patients ≥ 18 years-old who received PEG-Asp for B- or T-ALL at the University of Virginia between 2015 and 2020. The primary outcomes were the incidence of thrombosis and bleeding events. All patients received prophylactic AT3 repletion for activity level <60% & cryoprecipitate for fibrinogen <100mg/dL. None received prophylactic anticoagulation. All received prednisone during induction at a median daily dose of 1 mg/kg. Results: We identified 57 patients who received PEG-Asp for ALL. Median age was 32 years (range 18-63). Five patients (8.8%) had a thrombotic event during induction versus five (16%) during post-induction. Four patients (7%) had a bleeding event during induction versus five (10%) during post-induction. The most common type of thrombosis was deep venous thrombosis, with the majority being catheter-associated. Pulmonary embolism and CNS thrombosis were less common. During induction, the median time to thrombotic event was 18 days after last PEG-Asp administration. 60% and 80% of patients received AT3 and cryoprecipitate, respectively. During post-induction, the median time to thrombotic event was 58 days after last PEG-Asp administration. 38% and 63% of the patients received AT3 and cryoprecipitate, respectively. There was one episode of major bleeding during induction and six during post-induction. Conclusions: Though the increase in thrombotic risk in adult patients receiving PEG-Asp is well-characterized, rates of reported thromboses vary widely. Studies examining bleeding risk associated with PEG-Asp regimens are even scarcer and with variable outcomes. There was a significant occurrence of both thrombotic and bleeding events associated with administration of PEG-Asp. More investigation into the relative thrombotic and bleeding risks associated with PEG-Asp is needed to determine optimal antithrombotic interventions in adult patients with ALL.