In a series of 887 cases who underwent visceral, orthopedic or vascular surgery and who received systematic post-operative prophylactic anticoagulant treatment (calciparine S.C. or in 4.8% of cases low dose heparin IV), the author reports 31 accidents (3.5%). These included 9 thromboembolic disorders with 2 deaths (0.45%) due to pulmonary embolism, 19 hemorrhagic episodes (2.14%) with 2 deaths, and 3 cases of intolerance to heparin (0.34%): 2 cases of uncomplicated thrombocytopenia and 1 case of white clot successfully treated surgically. In spite of the good results obtained as far as prevention of thromboembolic disease is concerned, this study confirms the significant frequency and severity of iatrogenic accidents. These may be reduced partly by greater care in the prescription and execution of this treatment, but it is impossible to completely avoid them; it is therefore desirable in certain cases to avoid systematic prophylactic treatment by using other first line methods such as early mobilisation, elastic contention, hemodilution or indeed in certain cases the insertion of a vena cava filter. Moreover, in 11 out of 19 patients who presented a hemorrhagic complication of heparin therapy, the insertion of such a filter was judged indispensable in order to avoid possible pulmonary embolism favored by stoppage of anticoagulant treatment.