57 Cases of Portal vien 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. Sonographicfindings revelaled echogenic thrombus in the dilated portal vein. Echogenecity of thrombus was similra to the surrounding liver parenchyma. Thrombus was mainly located in the intrahepatic branch and main portal vein. 3. The location of thrombus in hepatocellular cardinoma was related to the location of tumor, and frequently extended to the main portal vein(68.9%). Incidence of thrombosis in hepatocellular carcinoma revealed 49 out of 157 cases, but prospective study showed 42 out of 84 cases(50%). Thrombosis was more common in large sized ill-defined diffuse infiltrative hepatocellular carcinoma. 4. Computed tomography(only 15 cases analyzed) findings revealed low density in the portal vein in all the cases and periportal enhancement in 10 cases on post-enhancement scan. 5.C llateral circulations were largely detected at the porta hepatis and gallbladder fossa. The detection rate was lower on the ultrasonography than onthe computed tompgraphy or angiography.