OBJECTIVE. The purpose of this study was to determine whether differences exist in baseline flow velocities in the main portal vein and the stent after the creation of transjugular intrahepatic portosystemic shunts with 10- and 12-mm Wallstents. SUBJECTS AND METHODS. We used Doppler sonography to determine baseline flow velocities in the stent and the main portal vein in 80 patients (38 patients with 10-mm Wallstents dilated to 10 mm and 42 patients with 12-mm Wallstents dilated to 12 mm) who had undergone creation of trans jugular intrahepatic portosystemic shunts without complications. RESULTS. We found no significant difference in the maximum flow velocity in the stent between the patients with 10-mm stents (160.3 ± 34.3 cm/sec) and those with 12-mm stents (164.4 ± 33.8 cm/sec). We also found no significant difference in the minimum flow velocity in the stent between the 10-mm group (132.4 ± 28.9 cm/sec) and the 12-mm group (126.7 ± 28.3 cm/sec). However, flow velocity through the main portal vein was significantly higher in the patients with 12-mm stents (53.6 ± 18.4 cm/sec) than in those with 10-mm stents (45.1 ± 13.8 cm/sec) (p < .03). CONCLUSION. After creation of transjugular intrahepatic portosystemic shunts, baseline flow velocities in the main portal vein in patients with 12-mm stents exceeded those in patients with 10-mm stents, although neither maximum nor minimum flow velocities in the stent differed between these two groups of patients. These findings suggest that criteria for shunt malfunction that use flow velocity in the main portal vein may need modification when 12-mm stents are being evaluated.