The frequency of recurrent cerebral ischemia and death was determined prospectively in 36 patients who presented with ischemic stroke and had atrial fibrillation. Patients were followed an average of 2.3 months (range, 3 weeks to 9 months). The recurrence rate for cerebral ischemia was 33%, and the mortality rate was 22%. A beneficial effect of anticoagulation, given nonrandomly, was observed when we compared treated versus untreated patients followed for a similar length of time. Nine patients (25%), however, had CT evidence of hemorrhage associated with cerebral embolic infarction.