The term radioembolization defines those procedures in which intra-arterially injected radioactive microspheres are used for internal radiation purposes. The aim of this procedure is to selectively target radiation to liver tumors and to limit the dose to the normal liver parenchyma. The yttrium-90 microspheres delivered through the hepatic artery are implanted into liver tumors in a ratio ranging from 3:1 to 20:1 as compared to a normal liver parenchyma. The principles of radioembolization are fundamentally different from the conventional embolization of liver cancer through transarterial embolization or chemoembolization. A work-up, involving computed tomography scanning, contrast-enhanced magnetic resonance imaging and hepatic angiography, is essential for assessing the appropriateness of the patient for yttrium-90 treatment. A simulation of the procedure, carried out with technetium-99m-labeled macroaggregated albumin particles which approximate the size of the microspheres, is used to identify the shunting of microparticles to the lungs or the gastrointestinal tract, thus helping in patient selection. Excellent periprocedural care, discharge planning and follow-up are essential in assessing treatment response and ensuring that the short-term side effects of radioembolization are adequately managed. In the management of hepatocellular carcinoma and metastatic tumors, the ever increasing literature regarding radioembolization shows that this is an effective treatment, improving survival with a low incidence of side effects. In bile duct tumors, radioembolization can only be used as a palliative treatment for intrahepatic cholangiocarcinoma; some recent studies have reported good safety and efficacy rates and low complication rates, with median survival ranging from 9 to 22 months