Portal vein thrombosis was thought to be a common complication of liver cirrhosis in the past. The incidence of angiographically demonstrable portal vein thrombosis was studied in 708 consecutive patients with unequivocal cirrhosis seen in the past 10 yr in whom either transhepatic portography or superior mesenteric arterial portography clearly delineated the major portal vein system. Excluding 2 cases that were thought to be associated with past splenectomy, there were 4 cases of portal vein thrombosis related to cirrhosis, all in a decompensated stage. The calculated incidence of portal vein thrombosis was 0.573% of all cirrhotic patients without splenectomy in the past. They constituted 23.5% of the 17 cases of extrahepatic portal vein obstruction encountered during the same period. There were 78 cases of idiopathic portal hypertension similarly studied angiographically, and the incidence of portal vein thrombosis unrelated to splenectomy was 2.86%. A statistical survey based on 247,728 necropsies recorded in the Japan Autopsy Registries of 1975-1982 showed a 0.05489% incidence of portal vein thrombosis and a 6.58857% incidence of cirrhosis of all types among them, suggesting that portal vein thrombosis is not a common complication of cirrhosis in Japan in recent years.