This study was performed to evaluate the feasibility and clinical impact of intraluminal and endovascular high-dose-rate iridium-192 brachytherapy on the treatment of HCC lesions growing into biliary trees, portal veins and the inferior vena cava. HCCs involving biliary trees in 2 patients, the main and/or first-order portal veins in 3 patients, and the inferior vena cava in 2 patients. Brachytherapy was percutaneously performed with a 5F applicator, which was placed adjacent to the lesions. A mean total dose of 23 Gy (range, 5-7 Gy/fr) was irradiated (at a 5 mm radius) to the biliary or the portal venous tumors. A total dose of 10 Gy (5 Gy/fr) was given to the caval tumors. External-beam radiotherapy was combined in 2 patients with caval lesions, stent placement in 2 patients with biliary lesions and hepatic arterial infusion chemotherapy in 5 patients. There was no major complication except hemobilia, which ceased after placing a PTCD tube in the bile duct in one patient. All tumors were significantly reduced in size and remained controlled during the period of patients' survival. Complete tumor necrosis was histologically proved in 2 autopsy cases having biliary lesions. The median survival was 13 months. Intraluminal and endovascular high-dose-rate brachytherapy appears to be a feasible, and effective procedure to treat advanced HCCs invading biliary trees, portal veins and the vena cava.