57 cases of portal vein thrombosis detected by ultrasonography were analized. The results were as follows: 1.Most common cause was hepatocellular carcinoma, showing 49 out of 57 cases(86%). 2. Sonographic findings revealedechogenic thrombus in the dilated portal vein. Echogenecity of thrombus was similar to the surrounding liverparenchyma, Thrombus was mainly located in the intrahepatic branch and main portal vein. 3. The location ofthrombus in hepatocellular carcinoma was related to the location of tumor, and frequently extended to the mainportal vein(68.9%). Incidence of thrombosis in hepatocellular carcinoma revealed 49 out of 157 cases, butprospective study showed 42 out of 84 cases(50%). Thrombosis was more common in large sized ill-defined diffuseinfiltrative hepatocellular carcinoma. 4. CT(only 15 cases analyzed) findings revealed low density in the portalvein in all the cases and periportal enhancement in 10 cases on post-enhanced scan. 5. Collateral circulationswere largely detected at the porta hepatis and gallblader fossa. The detection rate was lower on theultrasonography than on the CT or angiography.