OBJECTIVES: The risk of VTE disease in patients undergoing major orthopedic surgery (MOS) has extensively been studied in randomised clinical trials and more recently in cohort studies. Our objective was to estimate the risk of VTE disease in a much larger population and to calculate its economic consequences in hospital. METHODS: We conducted a retrospective study of the risk of occurrence and associated costs of VTE complications (including deep vein thrombosis (DVT) and pulmonary embolism (PE)) in patients undergoing MOS (including hip replacement, hip fracture and knee replacement). Data were obtained from the National inpatient Diagnosis Related Group (DRG) data base with exhaustive information concerning all the patients having undergone MOS in the year 1998 in France. These patients were stratified based on the presence or absence of a listed secondary diagnosis of DVT or PE. Length of stay in hospital and cost of inpatient care were then compared between patients with and without secondary diagnosis of VTE. RESULTS: 105,952 hospital stays, 37,034 and 58,135 were respectively recorded for hip replacement, knee replacement and hip fracture. Rates of VTE were recorded to be 1.4% and 2.6% for hip replacement and knee replacement respectively. For each primary Diagnosis Related Group, the length of stay was shown to be significantly higher in case of occurrence of VTE complications (19.1 days versus 15.1 for hip replacement, 18 days versus 15.2 for knee replacement, 21.4 days versus 13.8 for hip fracture). Consequently, total costs of inpatient care were substantially higher for patients with VTE complications. CONCLUSION: The rates of VTE observed from the National inpatient database provide information on the frequency of VTE complications after MOS in real setting. In patients undergoing major orthopedic surgery, the occurrence of VTE is associated with a longer hospital stay and higher cost of inpatient care.