In 1997, 50,000 hip replacements will be performed in the UK, and over 1 million worldwide. Venous thromboembolism is the most frequent serious complication following joint replacement; its effective and economic management is essential. Antithrombotic prophylaxis can be used to reduce the incidence of venous thromboembolic disease, which presents as either deep vein thrombosis or pulmonary embolism. A number of published studies have shown that prophylaxis against venous thromboembolism is financially beneficial in terms of reduced diagnostic and treatment costs. Cost-effectiveness studies have provided a comparison of the costs and consequences resulting from alternative prophylactic programmes. This article reviews the epidemiology of venous thromboembolism after total hip replacement, prophylaxis against it and a model for cost-effectiveness analysis. Its aim is to highlight inadequacies in the available data and areas of uncertainty within the model that require further research. Pharmacoeconomic studies published to date have all used a similar framework to allow prophylactic options to be compared. However, assumptions made about the frequency of clinical disease have varied widely between studies. This degree of uncertainty calls into question the validity of reported incremental cost savings between treatments. Some studies have also failed to address the cost of complications resulting from the prophylactic method under consideration. Future studies must carefully consider the validity of their models, understand the limitations on current knowledge of outcome rates, and carefully consider all outcomes (both beneficial and detrimental) that result from the intervention.