Abstract: Objectives: Infection during the induction phase of childhood acute lymphoblastic leukemia (ALL) is a major cause of morbidity and mortality. Several studies have indicated that genetically determined low serum levels of mannose-binding lectin (MBL), a component of innate immunity, are associated with increased risk for infections in patients receiving chemotherapy. Thus, these patients have been proposed to be candidates for MBL replacement therapy. Methods: In a population-based cohort of 137 children with ALL treated at a single pediatric hematology-oncology center with an almost identical chemotherapy regimen, we studied the relationship between polymorphisms in the MBL gene (MBL2) and the MBL2 promoter and the risk of infections during the first 50 d of induction therapy. Results: No increased frequency of infection was seen for the children with genotypes encoding serum low levels of MBL. A higher incidence of fever (P < 0.004), infectious events (P = 0.025), days with neutropenia (P < 0.001) and a higher frequency of antimicrobial therapy (P = 0.0007) were seen in the young age group (<2.5 yr) compared with the older age group (≥2.5 yr), independent of the MBL genotype. Conclusions: MBL deficiency did not influence the frequency of infections in children receiving induction chemotherapy for ALL, not even in the youngest children (<2.5 yr) whom we found to have the highest risk for infections.