In a review of our series of patients with arteriovenous malformations (AVMs), a group with atypical angiographic and histopathological characteristics was discovered. Unlike the typical AVM, these lesions contained normal cerebral tissue between the abnormal vessels. We call these lesions diffuse AVMs, and think that this AVM represents one end of the AVM spectrum from a tight nidus to a diffuse lesion. The mean age of these patients was 18.1 years. Eight patients presented with an intracerebral hemorrhage, two with seizures, one with headache without hemorrhage, and one with ischemic symptoms compatible with vascular steal. Cerebral angiography revealed three AVMs to be 2 to 4 cm in diameter, four were 4 to 6 cm in diameter, and five were > 6 cm in diameter. Characteristic angiographic features included multiple small arterial feeders, small ectatic vessels in the malformation itself, multiple small draining veins, and a diffuse, puddling appearance of the contrast dye. Despite 16 operations in 11 patients, complete resection of the AVM was accomplished in only 8. The four patients with residual disease have received radiation therapy. Histopathology of the surgical specimens found AVM vessels interspersed among normal appearing neurons and white matter. Leptomeningeal angiodysplasia was noted when the cerebral cortex was involved. Gliosis was noted in some cases. Diffuse AVMs represent a difficult surgical challenge and recognition of the lesion aids in surgical planning.