Hepatocellular carcinoma (HCC) is one of the most common malignancies in the world. One serious complication is the invasion of the portal vein. To investigate the new invasion of the portal vein in HCC following treatment by transcatheter arterial chemo-embolization (TACE), 124 patients with HCC were screened by ultrasound, computed tomography and angiography. Fifteen patients were diagnosed with portal vein invasion (PVI) during the initial examination and were excluded from the study. Of the remaining 109 patients, 18 developed PVI. Fourteen were male and four were female. None of these 18 patients completely responded to TACE treatment and all were in recurrence. The median time for appearance of PVI after the first TACE was 212 days. The median interval between PVI and the last negative ultrasound examination was 100 days. Both were correlated with the degree of PVI. The only significant factor affecting the time until the appearance of PVI was the TACE treatment. After the development of PVI, eight patients continued with the TACE treatment, and three of these patients were also treated with portal vein local chemotherapy. The regression of PVI was observed in two patients. The median survival time after the discovery of PVI was 129 days. Factors affecting the survival time were performance state, Pugh classification, sex, the area of tumour invasion and continued treatment.