Plaster cast immobilisation following trauma is a major risk factor for the development of deep vein thrombosis. In our controlled, randomized and prospective study on patients with minor injuries incidence of DVT in conservatively treated out-patients with plaster cast immobilisation of the leg was 3.9% in the control group (n = 126) without prophylaxis. By s.c. self-application of LMV heparin once daily the number of DVT in the prophylaxis group (n = 115) was reduced to 0. No severe side effects of NMH were observed. We conclude that thromboprophylaxis with LMW heparin once daily up to now conspiciously reduced the risk of DVT in outpatients with plaster cast immobilisation of the leg.