BACKGROUND: Iron-deficiency anemia is the most common type of nutritional disorder. New strategies for the treatment of anemia are very important for its reduction. The aim of this study was to assess the efficacy and feasibility of cyclical iron supplementation as a strategy to reduce the prevalence of anemia among preschoolers. METHODS: A randomized controlled trial was performed in the entire population of under five-year-old children who attended government daycare centers in a small town in the State of Sao Paulo, Brazil. The children were randomly allocated into two intervention groups: the Weekly and Cyclical Groups. During a ten-month period, the Weekly Group (n = 51) received weekly doses of 30 mg elemental iron (40 doses) and the Cyclical Group (n = 48) received two cycles of 20 daily doses of 30 mg elemental iron separated by a four-month period (40 doses). RESULTS: Overall, at the end of ten months, the prevalence of anemia of the children on both supplementation regimens showed a significant decrease from 20.20% to 5.05% (p-value < 0.0005). There was no significant difference in the anemia between the two groups (p-value = 0.35). The mean hemoglobin concentration increased by 0.27 g/dL (p-value < 0.016) and 0.47 g/dL (p-value < 0.0005) in the Weekly and Cyclical Groups, respectively; again there was no significant difference between groups (p-value = 0.17). However, the cyclical regimen was easier to manage. CONCLUSIONS: Both supplementation regimens significantly reduced the prevalence of anemia however administration of the Cyclical Group was easier to carry out and control. CLINICAL TRIAL REGISTRATION NUMBER: NCT00992823.