The author points out the importance of angiography for study of collateral circulation, size, shape, and pedicle in cases of aneurysm of the anterior cerebral artery. For the surgical treatment the ligature of the internal carotid in the neck is discarted as useless. In aneurysm of the precommunicating and communicating portions of the artery that grow downwards it must be used sub-frontal approach; the fronto-sagital approach must be reserved for those aneurysms that grow upwards (communicating artery, distal portion of the anterior cerebral artery or its branches). Very important is the controlled hypotension, which must be used during the disection of the aneurysm's neck; once the ligature has been done the arterial tension must be brought up to normal, if necessary by means of intra-arterial transfusion. In cases where there is arterial spasm, verified by angiography, controled hypotension must not be used, as arterial hypotension with ischemia produced by spasm leads to arterial thrombosis, with fronto-callosum hemorrhagic infarctation and death. The author presents 10 cases of operated aneurysms of the commuunicatting-anterior cerebral system, with tree deaths and seven recoveries.