We report six cases of meningio-angiomatosis, a disorder of the cerebral cortex of probable malformative origin frequently associated with neurofibromatosis and either asymptomatic or associated with a seizure disorder. The patients, three males and three females, ranged from 10 to 70 years of age at diagnosis. The lesion was an incidental autopsy finding in two patients; four subjects had a seizure disorder which improved following surgical resection of the cortical lesion. In five instances the process was unifocal; one patient with neurofibromatosis had multifocal involvement. Grossly, the lesions were firm, sharply demarcated, transcortical plaques with leptomeningeal calcifications in five cases. The cortical plaques showed characteristic features of meningio-angiomatosis, i.e. a circumscribed, proliferating microvasculature with perivascular meningothelial cell proliferation and fibrosis. In five cases Alzheimer's neurofibrillary change in neurons was present both within the plaques and in the surrounding cortex. Neither senile plaques nor granulovacuolar degeneration were noted. Electron microscopy in one case demonstrated typical intraneuronal accumulations of neurofilaments with regular constrictions. Intracortical vessels lined by endothelial cells with tight junctions were surrounded by pericytes and meningothelial cells. The significance of neurofibrillary tangles described in a variety of disorders, and the factors stimulating their production in the present cases are unknown.