The authors describe an unusual complication after radiofrequency ablation of hepatocellular carcinoma (HCC). An 84-year old man, already operated of right hepatectomy for HCC, underwent radiofrequency ablation (RFA) of a new focal hepatic lesion in IV segment, under ultrasound (US) and computed tomography (CT) guidance. The procedure was carried out without any special difficulties or complications. Seven days later, the patient suddenly complained epigastric pain, progressive jaundice and sleepiness and an increase in cholestasis sierological parameters. A CT scan revealed thrombosis of the left side branch of the portal vein, with moderate bile ducts distension. The case described demonstrates how RFA may cause thermally mediated damage of the surrounding structures, due to unpredictable radio-frequency propagation. The interest of this case report is due to the fact that portal vein thrombosis did not occur immediately after the procedure, it happened without direct vessel injury by the needle and involved a vessel greater than 3 mm.