Parasitic infections are highly prevalent in the general population. Detecting a relationship between a parasitic infection and cancer is not an easy task; it requires epidemiological, microbiological and molecular biology techniques. In this article the important mechanisms by which parasitic infections may induce carcinogenesis are reviewed. The association between Schistosoma japonicum, Schistosoma mansoni and hepatocellular carcinoma is covered. The cause-and-effect relationship between the liver flukes Opisthorchis viverrini, Opisthorchis felineus, Clonorchis sinensis, and cholangiocarcinoma is also reviewed. The evidence Supporting the role of schistosomes and liver flukes in carcinogenesis is discussed. Finally the importance of the primary prevention of these parasitic infections with oncogenic potentials is emphasized. Copyright (C) 2002 S, Karger AG, Basel.