Population-based research is beginning to show clearly the devastating impact that Opisthorchis viverrini infection has on the Laos-descendent population of Northeast Thailand who love to eat uncooked meat and fish, one of which being the parasite's intermediate host: cyprinoid fish. Here, Melissa Haswell-Elkins, Paiboon Sithithaworn and David Elkins discuss the parasite's life cycle and epidemiology, highlighting the close relationship between this infection and bile duct carcinoma, which is a major cause of death among adults in rural Northeast Thailand.