Literature review and original data concerning the most common cause of inherited thrombophilia - activated protein C resistance have been presented. One hundred and three patients with confirmed venous thromboembolism have been investigated for activated protein C resistance with 2 ( nd ) generation "Diagnostica Stago" test. Activated protein C resistance has been found in 22.3 % cases. In the group of 70 healthy unselected men and women, matched by sex and age, this mutation has been found in 7.1% cases. Out of 101 patients with pulmonary thromboembolism confirmed by pulmoangiography or perfusion lung scan, 78 have been investigated by Doppler echocardioscopy in order to detect pulmonary hypertension after 1.5 months. Statistically significant correlation between age and pulmonary artery pressure has been found. No correlation between pulmonary artery pressure and activated protein C resistance has been detected.