Focal nodular hyperplasia (FNH) is a lesion of the liver in which a large anomalous artery is located within a region of hyperplastic hepatic parenchyma. Patients with FNH commonly have other lesions, often vascular in nature, in the liver or other organs. We have noted that these associated lesions almost always occur in patients with multiple FNH. We therefore studied 27 autopsied patients with FNH. All 13 with multiple FNH had other lesions such as hemangioma of liver, meningioma, astrocytoma, telangiectasis of the brain, berry aneurysm, dysplastic systemic arteries, and portal vein atresia. One patient had several of these lesions including multiple FNH, meningioma, astrocytoma, vascular malformation of the brain stem, and hemangioma of the liver. In contrast, among the 14 patients with solitary FNH there were no associated lesions, except for hepatic hemangioma in one patient. The prevalence of this syndrome was estimated by examination of 2500 serial autopsies and autopsies with various components of the syndrome. On review of 73 consecutive autopsies with meningioma, three had multiple FNH, compared with seven of 2500 consecutive adult autopsies (P less than 0.001). Multiple FNH was found in two of 83 autopsies with astrocytoma (P less than 0.05) and in one of 139 autopsies with berry aneurysm (not significant). We describe a telangiectatic subtype of FNH which occurs in this syndrome as well as in a minority of patients with solitary FNH. The existence and character of this syndrome suggest that there may be an underlying systemic abnormality in some patients having components of the syndrome. Investigation of patients with multiple FNH lesions may reveal significant treatable lesions.