Although angiographic changes of fibromuscular dysplasia (FMD) of the carotid artery are regularly noted, histologic confirmation is rare. We therefore reviewed all patients with a histologic diagnosis of FMD affecting the internal carotid artery who were seen at our institution over a 25-year-period. FMD of the internal carotid artery was a very rare autopsy finding and was detected in only 4 of 20,244 consecutive autopsies (0.02%). In an additional 6 patients FMD of the internal carotid artery was identified in a surgical specimen. All patients were female and their mean age was 53 years. Nine patients had the medial form of FMD and 1 the intimal form. By immunohistochemistry the lesions consist of proliferations of smooth muscle with a minor fibroblastic component. FMD was rarely limited to 1 carotid artery and multivessel involvement was present in 9 patients. In reference to this experience epidemiologic, pathologic, and etiologic features of FMD of the carotid arteries are discussed.