Resistance to activated protein C determined by factor V Leiden (FVL) is the most frequent inherited risk factor of venous thrombosis. The purpose of our work was to reveal the frequency of FVL in Slovak patients with venous thromboses, to characterise the nature of venous thromboses in this inherited thrombophilia, and to consider the screening approach to investigation of FVL in patients with venous thromboses. 350 patients with a diagnosis of venous thromboembolic disease from various regions of Slovakia were investigated. FVL, detected by polymerase chain reaction, was found in 128/350 (37%) patients with venous thromboses. 118/128 (92%) patients were heterozygous and 10/128 (8%) were homozygous carriers. In 108/128 (84%) patients with FVL the thromboembolic disease occurred spontaneously. Phlebothrombosis occurred predominantly in the lower limbs--117/128 (91%) patients, atypical localisations were rare. The first thromboembolic event was manifested before 40 years of age in 69% of patients. The family history was positive in 60/128 (47%) FVL carriers with thromboembolic disease. Recurrent thrombosis occurred in 30% of patients with FVL. In agreement with findings in other European countries, the prevalence of FVL was high in Slovak patients with thromboembolic disease. The investigation of FVL seems to be justified in patients before 40 years of age with venous thrombosis of lower limbs, in the absence of triggering factors and with a family history of venous thromboembolic disease.