OBJECTIVE: To evaluate the average duration of in-hospital treatment with fondaparinux 2.5mg prescribed for venous thromboprophylaxis in acutely ill medical patients and to describe the treatment population. METHODS: Prospective, observational, national, multicentre, epidemiological study, performed in France at the request of the Transparency Commission of the French National Health Authority (Haute Autorité de Santé). This is part of a larger study program that also included a study with similar design in the general practice setting. The hospital practice part of the study was conducted by hospital pharmacists who were asked to include the first 15 adult subjects hospitalized in a non-surgical ward for whom fondaparinux 2.5mg was initiated for prophylaxis. RESULTS: Fifty-three pharmacists (49.5%) included a total of 718 patients. The average age was 71 ± 16 years (47%<75 years old); 54% were women. For 41% of patients, duration of fondaparinux 2.5mg administration ranged from 6 to 14 days. Eighty-five percent of patients had at least one acute illness related to the prescription of fondaparinux 2.5mg for thromboprophylaxis. Ten percent of the population had at least one risk factor listed on the Case Report Form. Characteristics of patients from the hospital practice study differ from those included in the general practice part of the ArchiMed Study program. CONCLUSION: The hospital practice part of the ArchiMed Study, which is similar to "audits of practices", shows that the real-life conditions of prescription of fondaparinux 2.5mg in patients hospitalized are generally in line with guidelines with respect to indication for thromboprophylaxis in acute medical illness.