One hundred cases of macroscopic supratentorial arteriovenous malformations are studied, along with the significant literature. On the basis of morphology, they are subdivided into straight-line, single-unit, multiple-unit, intra- and extracranial, venous-wall types, and one other of questionable type. The study does not confirm a relationship of pregnancy to bleeding. It does confirm the absence of vasospasm in association with these lesions, the increasing tendency of the lesion to bleed the smaller it is, the equal sex distribution, the peak incidence in the patient's fourth decade, the lack of significance of family history, and the lack of associated vascular lesions. The study stresses the advantages of preopertive three-dimensional angiography, surgical magnification, and intraoperative serial angiography. It is emphasized again that the fistula itself must be removed or obliterated.