OBJECTIVE: To evaluate the mean duration of treatment course with fondaparinux 2.5 mg (ARIXTRA(®)) in the setting of ambulatory general medicine, with respect to its indication in thromboprophylaxis for medically ill patients and to describe the population treated. METHODS: Observational, prospective, national, multicenter, pharmaco-epidemiological study, performed in France, at the request of the Transparency Commission (a division of the French Health Regulatory Authority). The general practitioners had to include the first three adult patients, considered as patients at high risk of venous thromboembolic events and immobilized for acute medical illness, treated with initiation of thromboprophylaxis by fondaparinux 2.5 mg. RESULTS: Two hundred and seventeen general practitioners included 840 patients. The mean age of patients was 63.6±18.1 years, and 63% of patients (n=520/831) were females. The real total administration duration of the treatment by fondaparinux 2.5 mg was known for 797 patients and was 15.8±12.4 days on average (range: 1-90 days, median: 10 days). In 40% of patients, the duration ranged from 6 to 14 days [duration consistent with the summary of product characteristics (SmPC)]. Among the 834 patients analyzed, 569 (68%) suffered from at least one acute illness and had at least one risk factor for venous thromboembolism (VTE). The indication did fully comply with the summary of product characteristics of fondaparinux 2.5 mg in 52% of the patients (n=434/834 patients). CONCLUSION: The results of the ArchiMed study support that the thromboprophylaxis treatment with fondaparinux 2.5 mg in ambulatory general medicine, and the associated medical conditions were usually consistent with the SmPC or guidelines. However, a difference was found for the duration and the initial indication, in situations that may be regarded as presenting a risk by the prescriber.