The clinical importance of medical complications in stroke rehabilitation is well recognized. However, the epidemiology, management and prevention of rehabilitation related medical complications and comorbidities receive little research attention in physiatry. Venous thromboembolism in stroke rehabilitation remains a serious problem, yet rigorous studies of risk, prevention, outcome and functional impact are lacking. This three-center trial will examine both the clinical and epidemiological aspects of deep vein thrombosis (DVT) prevention in the stroke rehabilitation population. The clinical study is a randomized placebo controlled trial of unfractionated heparin (100 units/kg subcutaneously bid) for prevention of DVT. The medication trial will determine if an additional 28 days of low-dose heparin therapy beyond the first two-weeks after stroke onset is superior to placebo for DVT prevention during the same time period. The main outcome of DVT will be identified by clinical examination and serial venous duplex ultrasound measured weekly and one month after discontinuation of the trial medication. The epidemiological study will use multivariate logistical techniques to identify potential risk factors for DVT including demographic characteristics, medical comorbidity, severity of neurological impairment (NIH stroke scale and Fugl-Meyer score), functional disability (FIMSM instrument) and level of plasma coagulation activity (prothrombin fragment 1+2, thrombin- antithrombin complex and D-dimer). A pretrial research team consisting of the principle investigator, a research assistant and a nurse coordinator will be assembled. Goals of the one-year clinical trial development phase include finalizing the research design and protocol, development of research database, establishing a plan for statistical and interim analyses, coordinate pharmacy and blood flow services between centers and standardize plasma tests of coagulation activity. An annual subject pool of over 600 stroke rehabilitation patients from three centers will be available to participate in the three-year formal trial. A research study advisory council consisting or clinicians, researchers, an ethicist and two stroke survivors will oversee the development and implementation of the clinical trial. This clinical trial will determine the efficacy of low-dose heparin for DVT prevention during stroke rehabilitation and help clinicians identify those patients most at risk for venous thromboembolic complications.