Two cases of neurological injury during manipulation of the head and neck are described. In the first case, a 33-year-old woman, who had already had one chiropractic manipulation without ill effects, suddenly vomited during a second manipulation, became comatose, and died 3 days later. In the second case, a 48-year-old woman had manipulations which included forceful rotations of the head. During the "adjustment" she began to complain of headache and nausea, became unable to walk, and presented the clinical picture of Wallenberg's syndrome. In the ensuing 4 years, the headache continued, but most of the other neurological symptoms gradually subsided. The nature of these vascular accidents and the means of prevention are discussed.