BACKGROUND: Consensus Conferences and Guidelines for deep vein thrombosis prophylaxis have been published, which recommend the use of prophylactic heparins in patients with risk of venous thromboembolism (VTE). The aim of this study was the assessment of the prophylaxis of VTE and the adherence to accepted guideline recommendations throughout the hospital. METHODS: A cross-sectional study was carried out in a teaching hospital after guidelines were implemented. Patients' risk factors of deep vein thrombosis, risk categories of patients, and prophylaxis used in different wards were recorded. Appropriate adherence to the guidelines was analysed. RESULTS: Of 397 patients, prophylaxis was used in 231 patients (58%), and low-molecular-weight heparins (LMWH) were used in 224 of them (97%). Patients with prophylaxis had a higher mean number of risk factors (SD) than those without prophylaxis [3.1 (1.4) vs 1.9 (1.4); p < 0.05)]. Prophylaxis was used in 72% and 90% of moderate and high-risk patients respectively. Appropriate adherence to all guideline recommendations was observed in 42% of patients. Adherence to guidelines was high as regards the use of prophylaxis according to patients' risk factors (78%) and the use of appropriate types of prophylaxis (99%), but was low regarding appropriate heparin dosage (47%) and preoperative dosage (37%). Appropriate prophylaxis use was higher in critical care and surgical wards than in medical wards. CONCLUSION: Prophylaxis of VTE is generally used in risk patients, but appropriate adherence to guidelines is less frequent and variable among different wards. Continuing medical education, discussion and dissemination of guidelines, and regular clinical audit are necessary to improve prophylaxis of VTE in clinical practice.