In cases of cerebral vascular insufficiency there is a group in which insufficiency of the vertebral arteries can be recognized. The patient with this condition is usually over fifty years of age and complains of a variety of symptoms including dizziness or vertigo, diplopia and visual changes, transient weakness of the extremities, and sometimes a brief loss of consciousness. The clinical condition is readily explained by transient ischemia of the brain stem. Sometimes the symptoms can be provoked or aggravated by certain positions of the head on the neck. These include such mundane movements as are employed in watching an aircraft, hanging out the washing, and sitting in the barber's chair. In a few instances, the ischemic attack may be so consistently induced that the movement is recognized and avoided. It would appear that the position of the head on the neck in these patients might influence the vertebral arterial flow. Following a report of 3 cases, in 1 of which postmortem vertebral arteriography (...