Two hundred and thirty patients with intermittent focal cerebrovascular insufficiency were followed for periods varying from 1 to more than 5 years. A comparison was made as to the occurrence of cerebral infarction between those who received anticoagulant therapy and those who did not receive such treatment. Of 115 patients treated continuously, 4 (4 per cent) had a cerebral infarction. Of 40 patients who did not receive this treatment, 16 (40 per cent) had a cerebral infarction. Of 75 patients treated for a limited period (months), 24 patients (32 per cent) had a cerebral infarction months or years after discontinuance of anticoagulant therapy. The occurrence of intracerebral hemorrhage was the same in treated and untreated patients. It is concluded that this therapy is associated with a reduction in cerebral infarction in this particular category of cerebrovascular disease.