Rates of warfarin-associated major hemorrhage that are reported in randomized trials and observational cohorts are generally low. The published rates may be underestimated, however, because few patients older than 80 years of age are enrolled in studies, and few cohort studies include the initial phase of therapy, which is reported to have the highest risk of adverse events. In a recent study of 472 patients who were just starting anticoagulant therapy, 32% of the patients were older than 80 years of age, and 91% had at least 1 stroke risk factor. Elderly patients experienced major hemorrhage at a rate of 13.1 per 100 person-years, compared with 4.7 for their younger counterparts. The first 90 days of therapy, age =80 years, and international normalized ratio =4.0 were associated with increased risk. Within the first year, 26% of patients stopped taking warfarin largely due to safety concerns. Rates of major hemorrhage nd warfarin termination were highest among patients with CHADS2 scores of =3.