BACKGROUND: Idiopathic noncirrhotic portal hypertension (INCPH) is a rare disease in the Western world. As a result, little is known about the clinical characteristics and outcome of these patients. Survival in these patients is considered to be similar to that of the general population. AIM: To investigate the clinical manifestations, pathophysiology, outcome and determinants of survival in Western INCPH patients. METHODS: Multicentre cohort study of INCPH patients. RESULTS: A total of 62 patients were followed for a median time of 90 months (range 24-310). Initial manifestations leading to the diagnosis of INCPH were related to portal hypertension in 82% of the patients. Histological signs of portal blood supply disturbances were present in nearly all patients. During follow-up, 12 of 62 patients developed liver decompensation, of which four were considered for liver transplantation. One patient died in the context of variceal bleeding. Hepatocellular carcinoma was not observed during follow-up. A total of 23 patients died during follow-up, only four of them due to liver related mortality. The Kaplan-Meier estimates for overall survival were 100% (95% CI 95-100%), 78% (95% CI 67-89%) and 56% (95% CI 40-72%) at 1, 5 and 10 years respectively. Survival for INCPH was significantly decreased (P < 0.001) compared to survival of the general population. Ascites was an independent predictor of poor outcome. CONCLUSIONS: In comparison to the general population, survival in INCPH patients is poor. Mortality is related to associated disorders and medical conditions occurring at older age. Patients rarely die due to liver related complications. Patients with ascites have a poor prognosis.