A study of the frequency and severity of adverse events during hospital stays, based on a sample of US Medicare beneficiaries, was published in late 2010. Medicare provides healthcare coverage for people aged 65 and over, the disabled, and patients with renal impairment. One in 7 patients (13.5%) experienced a serious adverse event, and nearly half of these events were considered preventable. When extrapolated to the entire Medicare population in the United States, this corresponds to an estimated 15 000 deaths every month among the disabled and the elderly. About half of these deaths were due to drugs, especially anticoagulants. There are no studies of this type in France.