Occlusion of the basilar artery was demonstrated arteriographically in two cases. The symptomatology is described. Due to effective collateral circulation the patients survived and recovered from severe neurological deficits. One of the patients, clincally in a state resembling akinetic mutism for several weeks, not only survived but regained speech. To our knowledge this has not been reported in the literature previously. Our cases as well as similar ones of others showed, that for development of effective intrcranial collaterals the time, during which occlusion occurs, is clearly of importance. Development of collateral circulation also depends on the anatomy of the circle of Willis and a sufficient extracranial circulation.