Experimentally induced cerebral aneurysms in rats treated with unilateral ligation of the common carotid artery, deoxycorticosterone and salt hypertension, and beta-aminopropionitrile, were studied macroscopically and with light-microscopy. The material consisted of 13 aneurysms located on the anterior cerebral-anterior communicating arterial complex and one on the posterior cerebral artery. The findings were generally in accordance with that of spontaneous lesions in man. The results show the validity of these experimental aneurysms as a model for saccular cerebral aneurysms in man.