Eight patients with diffuse livedo reticularis and cerebrovascular lesions (Sneddon's syndrome) are reported. The disorder was inherited by autosomal dominant transmission in 3 cases. Multiple occlusions in medium-sized arteries were demonstrated by cerebral and hand arteriograms. Digital artery biopsies showed intimal hyperplasia in 7 cases and recanalized thrombosis in one case. Our findings are compared with an extensive review of the literature. Differential diagnosis with other vascular disorders, especially cerebral thromboangiitis obliterans and the corticomeningeal angiomatosis of Divry and Van Bogaert is considered. We conclude that Sneddon's syndrome is a new genetic and progressive arteriopathy, occlusive and noninflammatory, involving medium-sized vessels. The pathogenesis has yet to be elucidated.