Abstract Background Idiopathic portal hypertension is a rare cause of portal hypertension, frequently misdiagnosed as cryptogenic cirrhosis. This study evaluates specific findings at hepatic vein catheterisation or liver stiffness in idiopathic portal hypertension. Methods 39 cases of idiopathic portal hypertension patients were retrospectively reviewed. Hepatic vein catheterisation and liver stiffness measurements were compared to matched patients with cirrhosis and portal hypertension, and non-cirrhotic portal vein thrombosis, included as controls. Results Hepatic vein-to-vein communications were found in 49% idiopathic portal hypertension patients precluding adequate hepatic venous pressure gradient measurements in 12. In the remaining 27 patients, mean hepatic venous pressure gradient (HVPG) was 7.1±3.1mmHg. Only 5 patients had HVPG≥10mmHg. HVPG was markedly lower than in cirrhosis (17±3mmHg, p<0.001). Mean liver stiffness in idiopathic portal hypertension was 8.4±3.3kPa; significantly higher than in non-cirrhotic portal vein thrombosis (6.4±2.2kPa, p=0.009), but lower than in cirrhosis (40.9±20.5kPa, p=0.005). Only 2 idiopathic portal hypertension patients had liver stiffness >13.6kPa. Conclusions Patients with idiopathic portal hypertension frequently have hepatic vein-to-vein communications and, despite unequivocal signs of portal hypertension, HVPG and liver stiffness values much lower than the cut-off for clinical significant portal hypertension in cirrhosis. These findings oblige to formally rule-out idiopathic portal hypertension in the presence of signs of portal hypertension.