The prevalence of human liver cancer shows a broad spectrum of variation in distinct geographical regions, depending on different risk factors, and their pathogenesis is poorly understood. We study the significance of molecular alterations of K-ras gene in human liver carcinomas in a low-incidence region such as a Mediterranean area of Spain (Valencia and Gerona). Our results reveal a low incidence of K-ras codon 12 mutations in hepatocellular carcinomas (HCC) and a higher incidence in cholangiocarcinomas (CCC). Similar results have been obtained in high-risk areas. We conclude that K-ras gene mutations are not a major event in the malignant transformation of hepatic cells in this region of the Mediterranean but that molecular implications of hepatocellular and cholangiocarcinomas appear to be different. Int J Surg Pathol 8(4):267-270, 2000