Idiopathic thrombotic occlusion of the extrahepatic portal vein is one of the commonest causes of portal hypertension in adult Blacks. The condition occurs more frequently in men and may be accompanied by evidence of minor functional impairment of the liver. Associated pancytopenia is quantitatively related to the degree of splenomegaly. Assessment of a spectrum of variables of blood coagulation and fibrinolysis, while failing to shed light on the possible pathogenesis, does suggest a rational basis for thrombolytic therapy.