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Prescribing warfarin for atrial fibrillation depends in large part on the expected reduction in ischemic stroke risk versus the expected increased risk of intracranial hemorrhage (ICH). However, the anticoagulation decision also depends on the relative severity of such events. We assessed the impact of anticoagulation on 30-day mortality from ischemic stroke versus ICH in a large community-based cohort of patients with atrial fibrillation.We followed 13 559 patients with atrial fibrillation enrolled in an integrated healthcare delivery system for a median 6 years. Incident ischemic strokes and ICHs were identified from computerized databases and validated through medical record review. The association of warfarin and international normalized ratio at presentation with 30-day mortality was modeled using multivariable logistic regression adjusting for clinical factors.We identified 1025 incident ischemic strokes and 299 ICHs during follow-up. Compared with no antithrombotic therapy, warfarin was associated with reduced Rankin score and lower 30-day mortality from ischemic stroke (adjusted OR, 0.64; 95% CI, 0.45–0.91) but a higher mortality from ICH (OR, 1.62; 95% CI, 0.88–2.98). Therapeutic international normalized ratios (2–3) were associated with an especially low ischemic stroke mortality (OR, 0.38; 95% CI, 0.20–0.70), whereas international normalized ratios >3 increased the odds of dying of ICH by 2.66-fold (95% CI, 1.21–5.86).Warfarin reduces 30-day mortality from ischemic stroke but increases ICH-related mortality. Both effects on event severity as well as on event rates need to be incorporated into rational decision-making about anticoagulants for atrial fibrillation.