A 29-year-old woman died from a right hemispheric infarction caused by dissection and subsequent thrombosis of the internal carotid artery after chiropractic manipulations of the neck. Pathologic study of several arteries of muscular and elastic type revealed a mediolytic arteriopathy with widespread mucoid degeneration and cystic transformation of the vessel wall caused by segmental degeneration of smooth muscle cells of the tunica media. We hypothesize that mediolytic arteriopathy was a predisposing factor for the dissection of the internal carotid artery after chiropractic manipulations in our patient.