In the period 1968 to 1978, 83 vascular malformations (AVM's) were treated by operation: 65 were excised and 18 were managed by interruption of afferent arteries. Three cryptic AVM's (two in the thalamus and one in the caudate nucleus) were discovered during exploration of hematomas in normotensive young women. All three of these small malformations were detected on computerized tomographic scans; none was apparent on preoperative angiograms. Two of the four deaths in this series occurred after excision of large, high-flow fistulas; the proposed cause was restoration of normal perfusion pressure in a chronically ischemic hemisphere rendered incapable of autoregulation. The addition of operative adjuncts, in particular, bipolar coagulation and operative microscopy, has extended traditional indications for operation to include favorably situated AVM's that have not bled and certain AVM's situated in critical regions of the brain.