Centrosome duplication is controlled in a cell cycle-specific manner and occurs once every cell cycle, thereby ensuring the balanced segregation of chromosomes during the mitotic phase. Numerical or structural abnormalities can arise in the centrosomes of malignant cells. Under defective cell cycle checkpoint systems, cancer cells with abnormal centrosomes can survive and re-enter the cell cycle, promoting unbalanced chromosome segregation and genetic instability. We investigated the centrosome aberrations in 33 patients diagnosed with hepatocellular carcinoma (HCC), using fluorescent pericentrin immunostaining. We also studied the p53 mutation, proliferative activity, and DNA ploidy in these cases. In normal hepatocytes, one centrosome was identified per cell as a round dot, usually in the vicinity of the nuclear membrane. However, in cancer cells from HCC tissue, several patterns of centrosome abnormalities occurred, including supernumerary centrosomes and centrosomes with an abnormal shape and size. Although the frequency of abnormal centrosomes in each tissue was relatively low compared with previous reports in other cancers, nevertheless, centrosome aberration was found in 30 out of 33 HCC tissues. The percentage of tumor cells with abnormal centrosomes was significantly higher in the nondiploid tumors (15.8+/-15.9 per thousand ) than in the diploid tumors (5.4+/-5.1 per thousand ) (P<0.05), and tended to be higher in the tumors with p53 mutation (11.6+/-13.1 per thousand ) than in those with wild-type p53 (5.6+/-6.8 per thousand ). Furthermore, 82% of nondiploid tumors exhibited p53 mutation, whereas only 41% of diploid tumors showed p53 mutation. The percentage of tumor cells with centrosome abnormalities were not related to tumor stage, size or proliferative activity. Therefore, our results indicate that hepatic cancer cells, under centrosome aberration and a defective checkpoint system possibly caused by p53 mutation, have the potential for genetic instability and aggressive behavior. This potential effect occurs irrespective of the tumor size or stage.