Human fascioliasis is a parasitic zoonosis that affects the liver of human and herbivorous animals. In chronic cases, its diagnosis is confirmed by direct visualization of parasitic eggs in stool examination, by positive testing for Fasciola hepatica antigens in stools, or by direct observation of parasites by endoscopic retrograde cholangiography or surgery. In acute cases, serological reactions as immunoblothing or detection of parasite antigens in the blood are useful. The treatment of choice is triclabendazole. However, parasite resistance in animals, as well as in man, has been reported to this drug. We report four patients in whom the parasitic infection persisted despite a course of treatment with triclabendazole.