In cerebral amyloid angiopathy, the contractile elements of the leptomeningeal and cortical arteries are replaced by noncontractile amyloid beta protein. The incidence of amyloid angiopathy increases with advancing age. It is associated with Alzheimer's disease and spontaneous cerebral hemorrhage. The latter can have the characteristic acute computed tomographic appearance of a hematoma at the cortex-white matter junction with extension of blood into the subarachnoid, subdural, and intraventricular spaces. Multiple hemorrhages are frequent. Additional bleeding can occur after evacuation of the hematoma, and postoperative hemorrhage can occur after cortical biopsy. To elucidate the role of surgery in this condition, we have reviewed 20 consecutive operated cases of cerebral amyloid angiopathy. A first group of 8 patients with senila dementia underwent cortical biopsy without resultant hemorrhage. A second group of 6 patients in good clinical condition had delayed evacuation of a spontaneous cerebral hematoma from cerebral amyloid angiopathy because of the radiological misdiagnosis of a hemorrhage within a tumor. One patient died of a pulmonary embolism, and another had subsequent multiple hemorrhages that were ultimately fatal. A third group of 6 patients in poor neurological condition had the acute evacuation of a spontaneous cerebral hematoma to relieve intracranial hypertension. All died or were severely disabled. One had repeated hemorrhages which added a progressively more severe organic dementia onto an initial hemiplegia.(ABSTRACT TRUNCATED AT 250 WORDS)