Yttrium-90 microsphere therapy, which has become more common in recent years, offers an effective and safe radionuclide treatment option in the treatment of primary and metastatic liver tumors. The success of the treatment is directly related to the multidisciplinary approach of Nuclear Medicine and Interventional Radiology specialists, correct patient selection and personalized treatment approach. This guideline has been prepared to guide current applications of Y-90 microsphere therapy.