The authors studied the effects of surgery on hemocoagulation parameters (PT, PTT, PLT, Fibrinogen, AT III). 30 patients, undergoing extrahepatic surgery were observed. Measurements were performed before, during and immediately after procedure, and 24 hs and 48 hs later. Results showed a significant drop of AT III activity (p < 0.05) throughout the surgical procedure with a prompt reversal to normal values right after the end of it. Fibrinogen values continuously increased from the end of surgery (compared to intra-op values) (p < 0.05) up to 48 hs (p < 0.01). PTT values decreased at the end of surgery (p < 0.05) and returned to normal during the following 24 hs. No thromboembolic and hemorrhagic complications were observed during the postoperative phase, with all patients being discharged after surgical resolution of pathologies. In conclusion accurate monitoring of hemocoagulation parameters (especially AT III) seems to be useful in order to prevent thromboembolic and/or hemorrhagic complications during and after surgery.The authors studied the effects of surgery on hemocoagulation parameters (PT, PTT, PLT, Fibrinogen, AT III). 30 patients, undergoing extrahepatic surgery were observed. Measurements were performed before, during and immediately after procedure, and 24 hs and 48 hs later. Results showed a significant drop of AT III activity (p < 0.05) throughout the surgical procedure with a prompt reversal to normal values right after the end of it. Fibrinogen values continuously increased from the end of surgery (compared to intra-op values) (p < 0.05) up to 48 hs (p < 0.01). PTT values decreased at the end of surgery (p < 0.05) and returned to normal during the following 24 hs. No thromboembolic and hemorrhagic complications were observed during the postoperative phase, with all patients being discharged after surgical resolution of pathologies. In conclusion accurate monitoring of hemocoagulation parameters (especially AT III) seems to be useful in order to prevent thromboembolic and/or hemorrhagic complications during and after surgery