Flow volume in the azygos venous system was quantitated with Cine-phase contrast (PC) velocity mapping in volunteers and compared with patients with known portal hypertension, who were referred for transjugular intrahepatic portosystemic shunt (TIPS) placement. Subsequently, the TIPS-induced hemodynamic effects on portal and azygos flow were analyzed. To assess intra- and intersubject variability, flow in the azygos veins was measured in each of 10 normal subjects at three different times. Subsequently, portal and azygos flow was quantitated in 20 patients with portal hypertension, before and after TIPS placement. All imaging was performed on a 1.5-tesla magnetic resonance imaging (MRI) system. Azygos flow was measured transaxially at the midthoracic level. Cine-PC flow measurements of the main portal vein followed morphological evaluation of the portal venous system with axial and coronal breath-held magnet resonance angiogram. Azygos flow in normal subjects was characterized by high inter- and low intrasubject variability. Azygos flow in patients with portal hypertension was significantly higher (P < .001). Following successful TIPS placement in 18 patients, Cine-PC revealed a mean decrease in azygos flow of 46.3% (P < .001) and a 134% (P < .001) increase of portal flow. Reflecting the complexity of portal hemodynamics, there was no correlation between the changes in the portal and azygos systems. In 2 patients with early occlusion of TIPS, documented invasively, portal and azygos flow values remained largely unchanged. Cine-PC enables the noninvasive, quantitative assessment of flow within the azygos venous system. Azygos flow was found to be markedly elevated in patients with portal hypertension. Combined portal and azygos PC flow measurements quantitate the therapeutic effect of TIPS placement.