OBJECTIVES: Thrombosis of the portal venous system (PVS) may complicate cirrhosis, pancreatitis, malignancies, and hypercoagulable states. Computed tomography (CT) scanning can diagnose thrombi present in the lumen of the PVS, but is probably insensitive. Endoscopic ultrasound (EUS) may be a more sensitive test for diagnosing PVS thrombosis (PVST). We sought to determine the accuracy of EUS for the diagnosis of PVST. METHODS: Using a retrospective analysis of patients' studies retrieved from a database at Massachusetts General Hospital, we determined the sensitivity and specificity of EUS in 16 patients with PVST and 29 without PVST as proven by surgery and/or CT scanning. All patients underwent a linear EUS exam of the PVS and the results of the EUS report were used as the basis of the study. RESULTS: The sensitivity of EUS for the finding of PVST was 81% in 13 of 16 patients and the specificity was 93% in 27 of 29 patients with an overall accuracy of 89% (40/45). In an additional group of 11 patients, EUS demonstrated the presence of a PVST that was not detected by CT scanning. CONCLUSION: Linear EUS is a highly sensitive and specific test for PVST.