Background This study evaluated the clinical application of CT guided 125iodine implantation in patients with portal vein tumor thrombus in primary hepatocellular carcinoma.Methods The ten patients (9 males and 1 female,aged from 36 to 72 years) with portal vein tumor thrombus accompanying hepatocellular carcinoma had been treated with comprehensive therapy including surgery,transcatheter arterial chemoembolization,radiotherapy ablation,microwave ablation or percutaneous ethanol injection.The average diameter of each tumor thrombus was 21.5 mm×30.5 mm.Seeds of 30 MBq 125I were implanted 5 mm apart within the portal vein tumor thrombus.The follow-up after 4 months included enhanced spiral CT.Results CT screening of the tumours indicated that 4 out of 10 patients showed complete response to the therapy,5 partial response and 1 stable disease.Adverse effects included aggravated abdominal dropsy and temporarily increased transaminase,which were controlled by medical management.Severe complications such as haemorrhage,biliary fistula,hepatic abscess,pancreatic fistula and hepatic function failure were not observed.Implanted seeds migrated to lung and left hepatic lobe in 1 case.Conclusion CT guided implantation of 125iodine seeds,can effectively treat portal vein tumor thrombus accompanying hepatocellular carcinoma with minimal damage and few complications.