A syndrome which occurs as a result of the occlusion of the basilar artery. It may be caused by atherosclerosis, embolism or hemorrhage. Clinical signs include dizziness, headache, vomiting, hemiparesis or hemiplegia, dysarthria, dysphagia, blurred vision and loss of consciousness. The clinical course is variable and is dependent upon the extent of the occlusion and the location of the clot along the basilar artery which determines the resultant neurologic impairment. Prognosis is dismal in cases where a complete occlusion occurs with rapid deterioration of neurological function.