Thromboprophylaxis for liver surgery can be commenced either preoperatively or postoperatively. Despite a clear trade-off between thrombosis and bleeding in liver surgery patients, there is no international consensus when thrombosis prophylaxis should be commenced in patients undergoing liver surgery. As far as we know, there are no prospective randomized trials in this field, and current guidelines are unfortunately based on very low quality evidence, that is, a few retrospective studies and expert opinion. Both American and European thromboprophylaxis guidelines for abdominal cancer surgery support the preoperative initiation of thromboprophylaxis, but these guidelines do not specifically address the increased bleeding risk associated with liver surgery. On the contrary, Dutch guidelines recommend postoperative thromboprophylaxis only, because of lack of evidence for preoperative thromboprophylaxis. Traditionally, many liver surgery units have been reluctant in using preoperative thromboprophylaxis due to the potentially increased risk of bleeding complications. Enhanced Recovery After Surgery (ERAS) Society Guidelines recommend preoperative thromboprophylaxis in liver surgery, but the guidelines provide no supporting evidence for this recommendation. Overall, the amount of evidence is scarce and somewhat contradictory in this clinically relevant field of thromboprophylaxis in liver surgery. The aim of this study is to compare pre- and postoperatively initiated thromboprophylaxis regimens in liver surgery in a randomized controlled trial.