Intra-arterial injection of radioactive Lipiodol has shown promising results in patients with hepatocellular carcinoma (HCC) and portal obstruction. The aim of this prospective, randomized trial was to compare the efficacy and tolerance of 131I-labeled Lipiodol and chemoembolization for the treatment of patients with HCC. From September 1990 to September 1993, 142 patients (135 men, 7 women; age: 65 ± 6.6 years) were randomly assigned to treatment groups and given either intra-arterial injections of 131I-labeled Lipiodol (60 mCi; 2.2 GBq) (n = 73) or chemoembolization (70 mg cisplatin) (n = 69). Subsequent injections were given at 2, 5, 8, 12, and 18 months. Tumor response was assessed on the basis of tumor size and serum α-fetoprotein levels. Patient tolerance was assessed clinically and angiographically. Survival rate was the main end-point. A total of 129 patients (65 in the 131I-labeled Lipiodol group and 64 in the chemoembolization group) were available for analysis; 13 were excluded, mainly because of portal vein thrombosis. The two groups were comparable. Actuarial survival curves were not significantly different between the two groups. Overall survival rates at 6 months, 1, 2, 3, and 4 years were 69%, 38%, 22%, 14%, and 10%, and 66%, 42%, 22%, 3%, and 0% in the 131I-labeled Lipiodol and chemoembolization groups, respectively. Reduction in tumor size was similar for the two groups, with complete response in 1 and 0 patients and partial response in 15 and 16 patients in the 131I-labeled Lipiodol and chemoembolization groups, respectively. Tolerance was significantly better in the 131I- labeled Lipiodol group both clinically (3 severe side effects vs. 29 in the chemoembolization group; P < .001) and angiographically (1 arterial thrombosis vs. 10 in the chemoembolization group; P < .01). In terms of patient survival and tumor response, radioactive 131I-labeled Lipiodol and chemoembolization were equally effective in the treatment of HCC, but tolerance to 131I-labeled Lipiodol was significantly better.