PURPOSE: We determined whether super selective radio embolization of the porcine kidney was technically feasible and evaluated histopathological changes in the treatment target zone (upper or lower renal pole), adjacent nontargeted kidney, and adjacent and distant organs after administering (90)Y labeled vs bland resin microspheres. MATERIALS AND METHODS: We performed super selective radio embolization with (90)Y resin microspheres in 1 kidney and with an equivalent number of bland microspheres in the corresponding pole of the contralateral kidney as a control. The aim was to achieve radio embolization of a target zone equivalent to approximately a third of the kidney volume. A pathologist independently graded macroscopic and microscopic changes in the kidney, and adjacent and distant tissue resulting from incremental increases (0.15 to 0.35 GBq) in implanted activity in 6 pigs. RESULTS: We recorded grade 4 histological changes in the treatment target zone (upper or lower renal pole) in 5 of 6 pigs after injecting (90)Y resin microspheres with evidence of nephron sparing effects in the adjacent renal tissue at the lowest activity. At activity greater than 0.3 GBq increasing damage was noted to adjacent renal tissue beyond the treatment target zone. No toxicity was evident in adjacent or distant organs. CONCLUSIONS: Delivery of highly targeted intra-arterial radiotherapy to the kidney is feasible and safe in the pig model. Further evaluation is warranted as a potential treatment for advanced renal cell carcinoma or for localized disease in patients who are not candidates for surgery.