Knowledge of the normal anatomy, most frequent variants, and congenital and acquired anomalies of the portal venous system is of great importance for liver surgery and interventional procedures such as creation of transjugular intrahepatic portosystemic shunts. Radiologic studies of the portal venous system include color Doppler ultrasonography (US), computed tomography (CT), magnetic resonance imaging, and arterial or direct portography. Among the most common branching variants of the portal vein are trifurcation, right anterior portal branch arising from the left portal vein, and right posterior portal branch arising from the main portal vein. Agenesis of the right or left portal vein is the most frequently reported congenital anomaly. Venous collateral vessels due to portal hypertension and cavernous transformation of the portal vein are best evaluated with cross-sectional imaging. Intrahepatic portosystemic, arterioportal, and arteriosystemic fistulas and associated perfusion anomalies have characteristic features at dual-phase helical CT. Color Doppler US is the single most useful tool for demonstration of aneurysms of the portal venous system and bland or neoplastic portal vein thrombosis. CT is also the best means of evaluating gas in the portal venous system, which is no longer an ominous sign and must be differentiated from aerobilia.