Portal hypertension is a severe, almost unavoidable complication of chronic liver diseases and is responsible for the main clinical consequences of cirrhosis. Measurement of the hepatic venous pressure gradient (HVPG) is currently the best available method to evaluate the presence and severity of portal hypertension. Clinically significant portal hypertension is defined as an increase in HVPG to >or=10 mmHg; above this threshold, the complications of portal hypertension might begin to appear. Measurement of HVPG is increasingly used in clinical hepatology, and numerous studies have demonstrated that the parameter is a robust surrogate marker for hard clinical end points. The main clinical applications for HVPG include diagnosis, risk stratification, identification of patients with hepatocellular carcinoma who are candidates for liver resection, monitoring of the efficacy of medical treatment, and assessment of progression of portal hypertension. Patients who experience a reduction in HVPG of >or=20% or to <12 mmHg in response to drug therapy are defined as 'responders'. Responders have a markedly decreased risk of bleeding (or rebleeding), ascites, and spontaneous bacterial peritonitis, which results in improved survival.