Abstract:Eleven elderly patients with arterial insufficiency of the brain (senile dementia, presenile dementia, transient ischemic attacks or recurrent strokes) were treated with an anticoagulant (bishydroxycoumarin) for periods varying from eight years to twenty‐four days. All 11 patients showed improvement. Interruption of treatment proved safe in 2 patients, harmful in 2 others, and fatal in 3 patients. In a case of Alzheimer's disease in which bishydroxycoumarin was stopped four times, the patient deteriorated each time the drug was discontinued and improved each time it was resumed.Anticoagulant therapy appears to be effective in relieving the symptoms of arterial insufficiency of the brain and preventing progression of disability. In a selected group of patients, considerable improvement may be expected. Once relief is obtained, discontinuing anticoagulant therapy (especially within two years) may be very risky since deterioration is likely to occur. The risks of using anticoagulants for this purpose are not discussed but probably they are the same as in the treatment of coronary artery disease. Not using anticoagulants may be more harmful than using them; discontinuation withdraws effective treatmen