Selective internal radiation therapy (SIRT) is used for the treatment of patients with liver tumors, especially for those with hepatocellular carcinoma (HCC) or liver metastases from various primary tumors. Currently this innovative treatment concept is recommended when established state-of-the-art treatment regimes have failed and tumor progression is noted or if the treatment has to be abandoned because of intolerable toxic effects. For SIRT small biocompatible microspheres (SIR-Spheres(R)) are labelled with the radioactive isotope 90Yttrium, a pure beta emitter, and are superselectively infused into the hepatic arteries. The microspheres are collected in the precapillary vessels in and surrounding the tumor. The beta radiation of 90Yttrium has an average penetration in tissue of approximately 2.5 mm and results in very high doses of radiation being selectively targeted to metastases providing protection to the surrounding healthy liver tissue. In this paper we review the results of SIRT in patients with hepatic metastases from colorectal cancer, breast cancer, neuroendocrine tumors and primary liver cancer (HCC).