Meningococcal disease incidence is highest in infants, but a significant burden of disease also occurs in children. In this Phase II, single-centre US study, 619 healthy children (2-10 years of age) received one dose of an investigational quadrivalent meningococcal CRM(197)-conjugated vaccine (MenACWY-CRM) or a licensed quadrivalent meningococcal polysaccharide vaccine (MPSV4). Immunogenicity was assessed using the serum bactericidal assay with human complement (hSBA) at 1 and 12 months post-vaccination. Local and systemic reactions were recorded for 7 days, all adverse events (AEs) for 1 month, and medically significant and serious AEs (SAEs) for 12 months post-vaccination. For all four serogroups, more MenACWY-CRM recipients achieved an hSBA titre >or=1:4 at 1 month post-vaccination (A: 82%; C: 83%; W-135: 95%; Y: 91%) compared with the group that received MPSV4 (A: 45%; C: 66%; W-135: 71%; Y: 61%); this difference persisted through to 12 months post-vaccination. Both vaccines were well tolerated. In children 2-10 years of age, MenACWY-CRM induced a higher immune response than that of MPSV4, and was well tolerated.