Idiopathic portal hypertension (IPH) is a rare cause of intrahepatic portal hypertension. Data on natural history and prognosis of IPH are limited. We sought to describe the complications and long-tem outcome of IPH by retrospectively studying 69 biopsy-proven cases of IPH. Mean duration of follow-up was 6.7 ± 4.6 years. All patients had evidence of portal hypertension (PH) at diagnosis, and 42% were symptomatic. Variceal bleeding (VB) was the most common manifestation. In those without bleeding at diagnosis, 74% had varices at first endoscopy. In those with large varices, the 1-year probability of first bleeding despite primary prophylaxis was 9%. The 1-year probability of rebleeding was 22%. Ascites and hepatic encephalopathy was documented in 26% and 7% of patients, respectively, at least once during the clinical course. The 1-year probability of developing portal vein thrombosis (PVT) was 9%, and 53% of patients receiving anticoagulation achieved recanalization. Human immunodeficiency virus (HIV) infection and VB at diagnosis were the independent predictors of PVT. Seven patients died (6 as a result of an IPH-related cause) and 2 were transplanted. Probability of liver transplantation–free survival was 82% at 10 years. Presence of a severe associated disorder and ascites as a presenting symptom were associated with poor survival. Conclusion: Variceal bleeding is a major complication of IPH. Using, in IPH patients, the same management approach for PH as in cirrhosis is safe and maintains a low incidence of first bleeding and rebleeding in IPH patients. PVT is a frequent complication, particularly in those with HIV infection. Despite several complications, overall survival of patients with IPH is considerably good. (Hepatology 2014;59:2276–2285)