We investigated the patterns of evolution of portal vein tumor thromboses (PVTTs) and the changes in serum tumor marker levels in untreated hepatocellular carcinomas. The mean time required for the subsegmental or lower-order branch PVTTs and the segmental PVTTs to reach the large portal vein was 120 and 101 days, respectively. The mean values of the serum alpha-fetoprotein levels markedly increased after the appearance of PVTTs from 1858.7 ng/ml to 6795.2 ng/ml.