During 1993, the prevalences of infection by intestinal protozoa and helminths (IPH) in the riverside schoolchildren population of two sectors of Valdivia river, with different levels of fecal contamination, were compared in relation to their contact with river water (swimming, bathing) and basic sanitation elements (BSE) of their houses: feces and garbage disposal, and water supply. Populations of children from sectors A (n = 418), with significatively greater (SG) total coliform most probable number (MPN), and sector B (n = 400), were examined. PAFS test was used for the stool examination of one sample, from each child. The global prevalence of infection by IPH was similar in A (74.8%) and B (72.5%) sectors. From 10 identified IPH, only Entamoeba histolytica and Hymenolepis nana showed prevalences of infection SG in sector A, than in sector B. The contact of the children with the water of the river showed association with SG prevalences for E. histolytica, Entamoeba coli and Endolimax nana in sector B and for E. histolytica in sector A. No sanitary condition for the different BSE contributed to SG prevalences for E. histolytica, Ascaris lumbricoides and Trichuris trichiura in both sectors, and for E. coli in sector B. The contact with the river water and the different BSE contributed to prevalences SG in 5 and 3 IPH in sectors B and A, respectively. The results suggest that a project in study for the development of a treatment plant of wastewater in sector A, could contribute to control infection by IPH. But, this measure must be associated with improvement of the BSE, health education, and application of chemotherapy measures for geohelminthosis in both sectors.