SummaryOcclusion of the basilar artery, whether complete or almost so, nowadays usually has an atheromatous basis. Once supposed to carry an almost uniformly poor prognosis, even complete obstruction is now known to be not necessarily fatal rapidly or invariably, and if the collateral circulation is effective there may be relatively little disability and quite long survival. At times affected patients may be males of early middle age, and if the clinical features or ancillary investigations lead to the suspicion of a posterior fossa neoplasm, the correct diagnosis will not be made until angiography. A similar pattern may be found with incomplete occlusion of high degree and two such cases are reported. The angiographic features are discussed in detail and reasons are given to justify the selective catheter technique used, which was without complications.