A generally accepted classification and documentation for cerebrovascular insufficiency are needed to eliminate controversies and misinterpretation in clinical studies on the spontaneous course of the disease and the outcome of patients receiving surgical or conservative treatment. The author proposes a clinical classification (stages I to IV) based on the affected vascular territory (A, B, C). The following findings should be included: 1. the number of diseased extracranial arteries (I to IV vessel disease), 2. the presence of ischemic brain lesions (CT, SPECT, RMI), 3. concomitant diseases or risk factors (hypertension, coronary heart disease etc.). Such morphological and functional staging makes possible the selection of comparable groups of patients for investigation.