PURPOSE: Congenital Iobar agenesis of the liver is a rare anomaly. We report five cases (three cases of right Iobar agenesis and two cases of left Iobar agenesis) and discuss the radiologic findings of this congenital anomaly. MATERIALS AND METHODS: Between July, 1992 and February, 1993, three cases of right Iobar agenesis and two cases of left Iobar agenesis of the liver were diagnosed by means of computed tomography(CT) and/or sonography. MR imging was performed in two patients, cholangiography in two, and digital subtraction angiography in one. RESULTS: The main findings of right Iobar agenesis of the liver were nonvisualization of the right portal vein and absence of liver tissue to the right of gallbladder. The findings of left Iobar agenesis were nonvisualization of left portal vein, absence of liver tissue to the left of the gallbladder, and absence of ligamentum teres. The ancillary finding of the Iobar agenesis was visualization of less than three hepatic veins. CONCLUSION: It is important to consider Iobar agenesis of the liver in differential diagnosis when imaging studies reveal abnormal portal vein branches, unusual position of gallblader, absence of ligamentum teres, and visualization of less than three hepatic veins.