Acquired activated protein C resistance (aAPCR) is seen more frequently in solid and hematological cancer patients. We aimed to investigate the presence of aAPCR and the frequency of clinically detectable thrombosis in sarcoma patients. Normalized activated protein C sensitivity ratio (nAPCSR), factor V Leiden (FVL) mutation, factor V (FV) levels and factor VIII (FVIII) levels were prospectively measured in 52 patients and in 52 healthy controls. Clinically detectable thrombosis was present in one patient (1.92%). Compared with healthy controls (106%), the sarcoma patients had significantly lower values of the nAPCSR at pre (87.25%) and post (94.35%) treatment period (P<0.0001). aAPCR was found as 4.2, 13 and 0%, respectively. The post-treatment FV levels (178.1 U/dl) were significantly (P<0.001) higher than the pretreatment levels (147.5 U/dl). Inverse correlation was found between post-treatment FV levels and nAPCSR values (r=-0.38, P<0.02). We found out a slightly increased frequency of venous thromboembolism in sarcoma patients. As an original finding which has not been reported previously in the literature, we also found out a decrease in the nAPCSR, persisting even after treatment. Thirdly, we found out that the significantly higher rate of aAPCR at the time of diagnosis totally disappeared after treatment. Blood Coagul Fibrinolysis 23:428-433 (C) 2012 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.