OBJECTIVES: Lung cancer patients are perceived to have a relatively high risk of venous thromboembolic events due to an activation of the coagulation system. In terms of activation of the coagulation system, the difference between video-assisted thoracoscopic surgery (VATS) and open lobectomies for primary lung cancer has not been investigated. The aim of this study was to compare the impact on the coagulation system in patients undergoing curative surgery for primary lung cancer by either VATS or open lobectomies. METHODS: In total, 62 patients diagnosed with primary lung cancer were allocated to either VATS (n = 32) or open lobectomies (n = 30). All patients received subcutaneous injections with dalteparin (FragminVR ) 5000 IE once daily. The coagulation was assessed pre- and intraoperatively, and the first 2 days postoperatively by standard coagulation blood tests, thromboelastometry (ROTEMVR ) and thrombin generation. RESULTS: The open lobectomies bled more than the VATS group and had a significantly lower platelet count (109/l) on postoperative Days 1 and 2 (198 vs 231 and 194 vs 243, respectively). The open group also had a higher international normalized ratio on postoperative Days 1 and 2 compared with the VATS group (1.21 vs 1.14 and 1.17 vs 1.09, respectively). There were no differences in thromboelastometry (ROTEMVR ) and thrombin generation parameters. None of the included patients developed venous thromboembolic events. CONCLUSIONS: In patients undergoing curative surgery for early-stage primary lung cancer, we observed a statistical non-significant differenceand a similar-sized minor impact on the coagulation system.