Portal hypertension is characterized by a chronic increase in portal venous pressure. This is initiated by an increased vascular resistance to portal blood flow. In advanced stages, however, blood flow increases and contributes to worsen and maintain portal hypertension. Increased pressure and blood flow within the portal system promotes the appearance and dilation of portal-systemic collaterals and oesophageal varices, which are responsible for the main complication of portal hypertension: massive gastrointestinal haemorrhage. In recent years there have been several major innovations in the evaluation of portal hypertension. These include the application of new endoscopic, ultrasonographic and haemodynamic techniques that allow a better evaluation of the portal hypertensive patient, especially when prophylactic medical therapy is considered. Ultrasonography is very useful to assess the patency of the portal vein. The association of a pulsed Doppler flowmeter increases its accuracy and allows the non-invasive estimation of the direction and magnitude of portal blood flow. In addition to the measurement of portal pressure, measurement of azygos venous blood flow has proven very useful in the haemodynamic evaluation of portal hypertension. Azygos blood flow represents an index of blood flow through gastro-oesophageal collaterals and varices draining in the azygos vein. Its main application has been the assessment of the effects of pharmacological therapy. Endoscopic measurements of variceal pressure, either by direct puncture or using non-invasive pressure gauges, have contributed significantly to the understanding of the mechanism of variceal haemorrhage. This technique allows the calculation of the variceal wall tension as the product of the transmural pressure at the varices and the radius of the varix.(ABSTRACT TRUNCATED AT 250 WORDS)