Twelve patients with portal vein thrombosis (PVT) associated with various disorders were examined. In 11 the diagnosis of PVT was made primarily by ultrasound. Endovenous lesions that presented with a mainly homogenous texture pattern of different echodensity could be clearly displayed, but failed to disclose specific echographic features that allow conclusive discrimination between blood clots (n = 7; mean diameter 13 +/- 1.7 mm) and venous tumor invasion (n = 5; mean diameter 24 +/- 12 mm). Thrombus resolution on therapy as well as cavernous transformation of the portal vein following acute PVT may be visualized by serial sonograms. Secondary findings in PVT that can be displayed by sonography include splenomegaly and superior mesenteric vein obstruction with intestinal ischemia. Real-time sonography has proved to be a valuable noninvasive method for the early diagnosis and follow-up of PVT.