We performed a meta-analysis of the English literature to assess the efficacy of four common regimes for thromboembolic prophylaxis after total knee arthroplasty: aspirin, warfarin, low-molecular-weight heparin (LMWH) and pneumatic compression. We reviewed 136 articles and abstracts published between January 1980 and December 1997. Papers not using routine venography and a lung scan or angiography to detect deep-venous thrombosis (DVT) and pulmonary emboli (PE) respectively, were excluded. Of the 136 studies, 23 with 6001 patients were selected.The incidence of DVT was 53% (1701/3214) in the aspirin group, 45% (541/1203) in the warfarin group, 29% (311/1075) in the LMWH group, and 17% (86/509) in the pneumatic compression device group. Intermittent pneumatic compression devices and LMWH were significantly better than warfarin (p < 0.0001) or aspirin (p < 0.0001) in preventing DVT.The incidence of asymptomatic PE was 11.7% in the aspirin group (222/1901), 8.2% (101/1229) in the warfarin group and 6.3% (24/378) in the pneumatic compression group. No studies with LMWH used routine lung scans. Warfarin and pneumatic compression were significantly better than aspirin in preventing asymptomatic PE (p < 0.05).The incidence of symptomatic PE was 1.3% (23/1800) in the aspirin group, 0.4% (2/559) in the warfarin group, 0.5% (2/416) in the LMWH group and 0% (0/177) in the pneumatic compression group. No statistically significant difference was noted between the above prophylatic regimes due to the very small incidence of symptomatic PE. measurements to document a propagation rate of 24% in the calf. Therefore prophylaxis after TKA is essential to prevent thromboembolic disease. Current prophylactic methods include pharmacological regimes such as aspirin, warfarin, and low molecularweight heparin (LMWH) and mechanical techniques such as intermittent pneumatic compression devices. 1,3,5,6,11,13-18,21-25,27,29,32-38. While pharmacological prophylaxis may be useful for the prevention of thromboembolic disease, associated morbidity such as haemorrhagic complications, routine phlebotomy, excessive cost, and dosing by injection after discharge may limit its use. 1,3,6,11,13,17,18,[22][23][24]29,[32][33][34][35][37][38][39] Pneumatic compression devices offer prophylaxis without such associated morbidity, but compliance by patients and nurses is essential. In addition, the type and duration of prophylaxis after hospital discharge are controversial.To determine the relative benefit of different types of prophylaxis after TKA, we performed a meta-analysis to assess the effectiveness of four commonly used regimes of thromboembolic prophylaxis: aspirin, warfarin, LMWH and intermittent pneumatic compression devices. A metaanalysis is a technique which follows a set of statistical methods that can integrate the results of individual studies. Thus, a quantitative summary of studies with an increase in statistical power and an improvement of the estimated size of an effect can be presented.