Different degrees of cerebral calcifications together with encephalofacial angiomatosis and seizure disorders characterize the Sturge-Weber syndrome. According to the observations reported in the literature, calcium deposits may be found in the wall of cerebral vessels, in the perivascular tissue and rarely within the neurons. Corresponding to the variety of localizations, the interpretation of the phenomenon remains obscure. Most theories postulate the role of a vascular factory and of a mesenchymal factor. Ultramicroscopic studies of the specimens obtained in 2 children with the Sturge-Weber Syndrome provided the following findings. A mucopolysaccharidic substance constitutes the substratum for the deposition of calcium. Small amounts of this substance and calcium deposits may be detected within the connective tissue of cerebral vessels precociously; later on, while increasing in size and calcium concentration, they obviously migrate to outside the vessels. Successively, the calcium deposits seem to localize around the blood vessels, In our opinion, these observations stress the role of a primitive vascular factor; consequently, anoxia, necrosis of cerebral tissues, and variation in the calcium ion concentration would act only as secondary factors.