Internal radiation therapy with subsegmental arterial injection of iodine 131(131I)-labeled iodized oil (Lipiodol; Laboratorie, Guerbet, France) was evaluated in 24 patients with nodular hepatocellular carcinoma (HCC) ranging from 2.5 to 8.0 cm in size. 131I Lipiodol (555 to 2220 MBq in 3 to 8 ml) was injected depending on the tumor size. Tumor reduction was seen in 88.9% of tumors smaller than 4.0 cm in diameter, 65.5% of tumors between 4.1 to 6.0 cm, and 25.0% of tumors larger than 5.1 cm. The tumor size reduction corresponded to the gradual drop of serum alpha-fetoprotein (AFP) levels and devascularization on follow-up angiography. Adverse reactions from treatment included fever, mild abdominal pain, nausea, and elevation of transaminases. These were mild and well tolerated by patients. This method provided long-term local control without complications related to the thyroid, lung, gastrointestinal tract, and bone marrow.