Toll-like receptor 4 (TLR4) is required for efficient recognition of bacterial infections. We investigated an association between 2 TLR4 mutations (Asp(299)Gly and Thr(399)Ile) and meningococcal disease in 197 patients and 214 healthy controls by allele-specific real time polymerase chain reaction and direct sequencing. Although the allele frequency was not higher in the overall patient population, a significantly higher frequency in the 40 patients younger than 12 months of age (P = 0.007) was observed. We conclude that TLR4 mutations represent a risk factor for meningococcal disease in this age group.