It is now reported that coronavirus disease 2019 ICU patients are at increased risk of thrombosis. Expert opinion and scientific societies recommend a higher dose of low-molecular-weight heparin, but definitive data is lacking. We report our adapted thromboprophylaxis practice of low-molecular-weight heparin administration in coronavirus disease 2019 ICU patients. One-hundred six measurements in 19 ICU patients were collected. Despite enoxaparin 60 mg once daily, only two measurements of the trough anti-Xa were in the upper end of prophylactic range. Anti-Xa activity peaks increased significantly after administration, but all measurements were under the optimal prophylactic ranges. Despite an adapted protocol, three of the 19 patients (16%) developed venous thromboembolism. We show in coronavirus disease 2019 ICU patients, despite higher prophylactic low-molecular-weight heparin administration due to body mass index, anti-Xa activity was well below peak serum levels in our cohort of critically ill coronavirus disease 2019 patients. This evaluation suggests the need for rapid studies on adequate thromboprophylaxis in these patients.