The incidence and forms of cerebral amyloid angiopathy were studied in 15 cases of Alzheimer's disease using Congo red staining and polarization. Thirteen cases showed slight to severe involvement; two contained no amyloid vascular degeneration. There was a correlation between the presence of amyloid-rich plaques and cerebral amyloid angiopathy (especially the plaque-like angiopathy) but no correlation with "amyloid-poor" senile plaques or Alzheimer's neurofibrillary degeneration.