Infectious complications are the leading cause of mortality in children with acute leukemia. Despite the fact that intestinal parasitosis is a rather frequent finding and a health problem in underdeveloped countries, in our experience the incidence of helminthic and protozoan infections among children with leukemia is uncommon. We analyzed 54 consecutive patients with leukemia in a period of 5 years, and only seven (12.9%) had intestinal parasites, four of whom died because of the infection or complication by the parasites. One hundred children without any malignancy were the control group, 26 (26%) of whom had intestinal parasitosis. When we compared the frequency of parasitosis in the control group with the children with leukemia and parasitosis, we found a statistical difference (p less than 0.05). We speculate that parasitic infections may reduce the risk of childhood leukemia.