Venous thrombo-embolic disease in neurosurgical and surgical intensive care units is a frequent disorder (between 4.3 and 43 per cent of patients according to studies). The treatment is often difficult. We carried out a retrospective study from January 1994 to September 1995 of 57 patients in neurosurgical and surgical intensive care who developed thrombosis of a sural vein and in whom anticoagulant at therapeutic doses was contraindicated. After a median follow up 14 days echography showed proximal extension of the thrombosis in 4 patients and distal extension in 3 others. Five cases of pulmonary embolism occurred during the follow up period, one of which led to death. No complications (pulmonary embolism or proximal extension of venous thrombosis) occurred in those patients receiving heparin at prophylactic doses (0/11 versus 8/46 in the non-heparin group; p = 0.13). No case of pulmonary embolus occurred in those patients with partial or complete regression of the thrombosis (0/21 versus 5/36 in the group with stable or extending thrombi, p = 0,05). Echographic monitoring enabled therapeutic modification in 5 cases. These results indicate that sural venous thrombosis in the context of neurosurgical and surgical intensive care is a potentially grave situation and that the prescription of anticoagulant therapy even at preventive dose should always be considered. Further, we propose regular echographic monitoring until the patient is mobile.