We have evaluated positron emission tomography (PET) scanning during sensory stimulation or during the performance of auditory, visually based or expressive language tasks (activation PET scanning) to determine its reliability in establishing the relationships of cerebral arteriovenous malformations (AVMs) to the ambient cortex in 10 patients. Five patients with a central AVM underwent activation PET scanning combined with three-dimensional MRI during vibrotactile stimulation of the contralateral hand, and 5 patients with AVMs in or around speech areas were similarly scanned during a language task. Vibrotactile stimulation identified the post-central gyrus, establishing the relationship of the AVM to the central region. The results of language activation were specific to the modality (visual, auditory, articulate) on which the task was based. Sensory PET activation scanning is reliable in identifying the pre- and post-central gyri and useful in assessing AVMs in and around the central region. A greater understanding of results in normal controls for specific visual, auditory, and expressive language tasks is necessary before language activation PET scanning can be confidently applied to clinical cases.