In medicine, portal hypertension is hypertension (high blood pressure) in the portal vein and its branches. It is often defined as a portal pressure gradient (the difference in pressure between the portal vein and the hepatic veins) of 5 mm Hg or greater. Many conditions can result in portal hypertension. In North America and Europe, it is usually the result of cirrhosis of the liver. However, in less industrialized parts of the world, climate permitting, the major cause is schistosomiasis.