Occurrence of some medically important flukes transmitted to man by eating of raw fish was observed at 18 localities of Nam Ngum water reservoir, an important source of fish for inhabitants of Vientiane Province, Laos. Cercariae of Opisthorchis viverrini were recorded in 0.9% of Bithynia siamensis goniomphalus examined but in the most populated sites, where the density of the snails was the highest up to 2.2% of the intermediate hosts were infected. Haplorchis cercariae were found in 2.0% of Tarebia granifera examined. O. viverrini metacercariae were found in flesh of four fish species (Hampala dispar. H. macrolepidota, Puntius gonionotus, Cyclocheilichthys repasson) from 9 localities with the highest prevalence (16%) in H. dispar. Metacercariae of Haplorchis pumilio and H. taichui were found in flesh of Hampala dispar, H. macrolepidota and Puntius gonionotus with the prevalence of infection 2-6%. Metacercarie of Stellantchasmus falcatus were localized in fins of Xenentodon canciloides. Domestic cats (Felis catus f. domestica) harbored the following trematode species: O. viverrini, H. pumilio, H. taichui, H. yokogawai, S. falcatus. Eggs of small flukes were found in stools of 44% of examined inhabitants of 3 villages and of the district center Thinkeo. The study revealed that the best predictor of the existence of small fluke foci and their species composition in the area studied was the second intermediate host-fish.