On the basis of theoretical rationale, heparoids and vitamin K antagonists are prescribed to prevent complications of venous thromboembolism (VTE, including pulmonary emboli [PE] and deep vein thrombosis [DVT]). They have been employed as the standard of care for treatment of VTE for over 40 years. Critique the evidence supporting the efficacy of anticoagulants for the treatment of VTE in reducing morbidity and/or mortality. This includes a search of reference lists and Medline. This includes studies concerning the diagnosis and incidence of PE and DVT, efficacy of anticoagulants in preventing complications, risks of anticoagulant therapy, and the costs of diagnosis and the treatment of VTE. I analyzed references cited in reviews and meta-analyses of VTE, and from Medline searches concerning diagnosis and treatment. The data quality and validity of studies depended on the consistency of findings and statistical significance of the data. No placebo-controlled trials of anticoagulants as treatment of PE with objective criteria for diagnosis have been published. Three randomized trials of anticoagulants vs no anticoagulants in DVT showed no benefit with heparin and vitamin K antagonists (combined all-cause mortality: anticoagulants = 6/66, un-anticoagulated controls = 1/60, P = .07). No placebo-controlled trials of low-molecular-weight heparins or thrombolytic drugs have been done; therefore, their efficacy in VTE depends entirely on randomized comparisons with unfractionated heparin. They have not been proven safer or more efficacious than unfractionated heparin. Thrombolysis causes more major and fatal bleeds than heparin and is no more effective in preventing PE. Diagnosing and treating VTE patients in the United States with anticoagulants costs 3.2 dollars to 15.5 billion dollars per year (1992 dollars). Bleeding and complications of angiography cause 1017-3525 deaths annually. Anticoagulants have not been proven efficacious or safe in VTE. The bleeding risks and other complications of anticoagulation are unacceptably high. The use of anticoagulants for patients with VTE should be reconsidered.