Twenty four patients with hepatocellular carcinoma who refused surgery or had unresectable tumor ranging 2.5 to 8.0 cm in size were treated with intrahepatic arterial injection of iodine-131-labeled iodized oil (I-131 Lipodol) in an attempt to achieve internal radiation of tumor. 555-2,220 MBq in 3-8 ml of I-131 Lipiodol was injected into the hepatic artery or proximal to the tumor feeding vessel depending on the tumor size. Tumor size reduction was observed in 88.9% of tumor smaller than 4.0 cm in diameter, 65.5% between 4.1 to 6.0 cm, and 25.0% of larger than 6.1cm, respectively. The tumor size reduction was corresponded to the gradual drop of serum AFP levels, decreased uptake on gallium-67 scintigraphy, and devascularization on follow-up angiography. Tumors having significant A-V shunts revealed further tumor growth. Adverse reactions from the treatment include fever, mild abdominal pain, nausea and elevation of transaminases. These have been mild and well-tolerated by the patients. This method was able to provide long term local control without complications related to thyroid, lung, GI tract and bone marrow.