In the study, to analyse a K-ras oncogene mutated at codon 12 in 24 patients with cholangiocarcinomas, four (16.67%) of them contained this point mutation. One of 4 was peripheral and the others were hilar tumors. There was no significant relationship between mutation and clinical features in terms of age, sex, endemic area, tumor location, tumor grading and pathological features. In our study, the incidence of K-ras codon 12 mutation in Thai patients with cholangiocarcinoma was lower than that found in British and Japanese patients. The discrepancy of incidence and type of the mutations, in different races and environment probably indicates that there is/are different etiologic mechanism(s) in the pathogenesis of cholangiocarcinoma.