The prevalence of intestinal parasitosis was investigated in a primary school located in Rubiao Junior, a peri-urban district of Botucatu, Sao Paulo state, Brazil, in order to assess the effect of treatment and practical measures of prophylaxis in the control of parasitic infections among 7-to-18-year-old school children of a low socio-economic status. The first series of parasitological examinations included 219 school children, of which 123 (56.1%) were found to be infected with one or more parasite species. Eighty-four children carrying pathogenic parasites were submitted to various anti-parasitic treatment schedules. We re-evaluated 75 (89%) students after 4 to 6 months postchemotherapy. The results indicate that the combination of treatment with prophylactic measures has been successful in the control of parasitic infections, since reinfection rates were generally low (≤5.3%), except for Giardia lamblia infections (18.6%), and a marked reduction on the prevalence rates was observed with a significant percentage of cure (≤73.1%) in children infected with most parasite species. The reasons for the apparent failure in the control of infections caused by Hymenolepsis nana and Strongyloides stercoralis are discussed.