BACKGROUND: Ascites is defined as the pathological accumulation of fluid in the peritoneal cavity. It is the most common complication of cirrhosis, which is also the most common cause of ascites. Viscosity is a measure of the resistance of a fluid to deform under shear stress. Plasma viscosity is influenced by the concentration of plasma proteins and lipoproteins, with the major contribution from fibrinogen. To our knowledge, the viscosity of ascitic fluid has not yet been studied.