['Critical injury has been associated with reduction in innate immune function in adults, with infection risk being related to degree of immune suppression. This relationship has not been reported in critically injured children.', 'Innate immune function will be reduced in critically injured children, and the degree of reduction will predict the subsequent development of nosocomial infection.', 'Children (≤18 years old) were enrolled in this longitudinal, prospective, observational, single-center study after admission to the pediatric intensive care unit following critical injury, along with a cohort of outpatient controls. Serial blood sampling was performed to evaluate plasma cytokine levels and innate immune function as measured by ex vivo lipopolysaccharide-induced tumor necrosis factor α (TNF-α) production capacity.', 'Seventy-six critically injured children (and 21 outpatient controls) were enrolled. Sixteen critically injured subjects developed nosocomial infection. Those subjects had higher plasma interleukin 6 and interleukin 10 levels on posttrauma days 1-2 compared with those who recovered without infection and outpatient controls. Ex vivo lipopolysaccharide-induced TNF-α production capacity was lower on posttrauma days 1-2 (P = 0.006) and over the first week following injury (P = 0.04) in those who went on to develop infection. A TNF-α response of less than 520 pg/mL at any time in the first week after injury was highly associated with infection risk by univariate and multivariate analysis. Among transfused children, longer red blood cell storage age, not transfusion volume, was associated with lower innate immune function (P < 0.0001). Trauma-induced innate immune suppression was reversible ex vivo via coculture of whole blood with granulocyte-macrophage colony-stimulating factor.'] Does innate immune function predict the development of nosocomial infection in critically injured children?