Backgroud/Aims: Idiopathic portal hypertension (IPH) is defined as portal hypertension with splenomegaly and hypersplenism in the absence of cirrhosis or obstruction of portal vein or hepatic vein. It has been recently suggested that hypercoagulable state and thromboembolic event of small portal veins have an important role in the pathogenesis of IPH. In this study, we evaluated the clinical and pathological characteristics of IPH. Methods: We reviewed clinical, endoscopic, radiologic and liver biopsy findings of 10 cases of IPH retrospectively. Results: The tests for antithrombin III deficiency, protein C deficiency, protein S deficiency, resistance to activated protein C, lupus anticoagulant, antiphospholipid antibodies, anticardiolipin antibodies were normal. Pathologic findings revealed portal vein dilatation (10/10), loss of portal vein (6/10), portal vein sclerosis (1/10), dilated megasinusoids (9/10), dilation of terminal hepatic vein (8/10), narrowing of terminal hepatic vein (2/10), hairline fibrous septa (1/10), and regenerative nodule (1/10). Conclusions: The pathologic finding of IPH showed various manifestations of obliterative portal venopathy although there was no hypercoagulable state.(Korean J Hepatol 2000;6:187-196)