The pre-surgery identification of patients at risk for the development of post-operative venous thromboembolism has not yet been achieved. It is a well recognized fact that major surgery without prophylaxis encompasses a high risk for thrombosis, in particular orthopaedic operations (hip/knee surgery approximately 50%) and abdominal surgery (approximately 20%). Other well-defined risk factors, though rarely occurring, are deficiencies of the major inhibitors of blood coagulation (i.e. protein C, protein S and antithrombin III). Less well-defined risk factors are a history of previous thrombosis, obesity, varicosis, cancer etc. In an attempt to identify patients at risk for thrombosis prior to surgery, several investigators have developed complicated risk predictors, i.e. formulae comprising combinations of coagulation test results and physical characteristics such as body weight. However, the clinical usefulness has only been demonstrated in two small studies evaluating gynaecological surgery patients. These prognostic indices have not, however, found general acceptance and are not used routinely. The importance of all these risk factors for patient management with regard to thrombosis prevention is relatively small. Irrespective of the absence or presence of identified risk factors, currently the majority of patients will receive some formal thrombosis prophylaxis. The major problem at present is the development of proximal vein thrombosis despite the best possible thrombosis prophylaxis (approximately 10% after hip surgery). Identification of these patients pre-operatively or in an early stage in the post-operative phase by single screening tests should be a major research issue. Furthermore, the development of a prophylactic regimen which eliminates proximal deep vein thrombosis is still desperately needed.