The hemodynamic features of gastric varices are not well documented. The purpose of this study was to investigate the nature of hepatofugal collateral veins, their origins, the direction of blood flow in the major veins and collateral veins, and portal venous pressure. To this end, 230 patients, mostly cirrhotic, who had esophageal or gastric varices, or both, demonstrated by endoscopy were investigated by portal vein catheterization. The findings were correlated with endoscopically assessed degrees of varices. Gastric varices were seen in 57% of the patients with varices due to portal hypertension. In most of the patients with advanced gastric varices, esophageal varices were minimal or absent. When patients with gastric varices were compared with those having predominantly esophageal varices, it was found that advanced gastric varices were more frequently supplied by the short and posterior gastric veins, they were almost always associated with large gastrorenal shunts, and portal venous pressure in patients with large gastric varices was lower. Chronic portal systemic encephalopathy was more common in patients with large gastric varices due to hepatofugal flow of superior mesenteric venous blood in the splenic vein than in patients with predominantly esophageal varices. Thus, the hemodynamics in patients with large gastric varices are distinctly different from those in patients with mainly esophageal varices, and such differences seem to account for the differing incidence of chronic encephalopathy and variceal bleeding.