OBJECTIVE To assess the accuracy of three-dimensional contrast-enhanced magnetic resonance angiography (3D CE MRA) in evaluating the portal vein involvement in patients with hepatocellular carcinoma. METHODS Ninety patients with hepatocellular carcinoma underwent 3D CE MRA of the portal venous system, using a high-field 1.5 T MR machine and a body coil and using Gd-DTPA as contrast material, before hepatic surgery or interventional therapy. The acquired source images of the examination were reconstructed into 3D MRA image similar to that of conventional X-ray angiography. The patency of the main, right and left portal veins was evaluated. A total of 270 veins were assessed. The patency was classified as normal or involved. The involvement included encasement, occlusion, and tumor thrombosis. The 3D CE MRA diagnoses were compared with the surgical-pathologic, intra-operative sonographic, and X-ray portographic findings. RESULTS 74 of the 75 involved portal veins and 188 of the 195 noninvolved portal veins confirmed by surgery or X-ray portography were detected by 3D CE MRA with an overall sensitivity rate of 99%, specificity rate of 96%, positive predictive value of 91%, and negative predictive value of 99%. The accuracy in diagnosis of the main portal vein was 100%. 3D CE MRA resulted in 7 false-positive interpretations involving 6 left portal veins and 1 right portal vein. One false-negative diagnosis was made on the right portal vein. CONCLUSION 3D CE MRA is quite accurate in evaluation of portal vein involvement in patients with hepatocellular carcinoma.