In clinical practice there are several conditions that are at relatively high risk of venous thromboembolism (VTE). However, not all patients included in the high risk category will actually develop VTE, and not all patients in the low risk category are protected against this eventuality. A high risk of VTE is associated with orthopedic or major surgery; a relative risk is associated with laparoscopic surgery, intermediate risk is associated, for instance, with oncology. In conclusion, individuals with deficiencies of natural anticoagulants, homozygotes due to mutation of Factor V Leiden or prothrombin and individuals with multiple risk factors may be defined as "high risk".