This study will examine whether the tendency to have thrombosis, or the formation of blood clots inside blood vessels, has a role in the development of pseudotumor cerebri (PTC). PTC causes symptoms and signs of isolated elevated blood pressure in the cranium, or covering of the brain. The disorder can lead to significant, negative effects on the visual system. Increased pressure of the cerebrospinal fluid, that is, fluid around the brain, is a factor, but the cause of the disorder is not clear. There has been documentation of clustering of PTC within families. It suggests that potential genetic polymorphisms-abilities to take on different forms-may become evident after exposure to conditions known to trigger PTC.