Rationale: Injurious agents often cause less severe injury in neonates as compared to adults. Objective: We hypothesized that maturational differences in lung inflammation induced by lipopolysaccharide (LPS) may be related to the nature of the nuclear factor B (NFB) complex activated, and the profile of target genes expressed. Methods: Neonatal and adult mice were injected with intraperitoneal LPS. Lung inflammation was assessed by histology, and apoptosis was determined by terminal deoxynucleotidyl transferase UTP nick end labeling (TUNEL). The expression of candidate inflammatory and apoptotic mediators was evaluated by quantitative real time polymerase chain reaction and western immunoblot. Results: Neonates demonstrated reduced inflammation and apoptosis, 24 hours after LPS exposure, as compared to adults. This difference was associated with persistent activation of NFB p65p50 heterodimers in the neonates in contrast to early, transient activation of p65p50 followed by sustained activation of p50p50 in the adults. Adults had increased expression of a panel of inflammatory and proapoptotic genes, and repression of anti-apoptotic targets, whereas no significant changes in these mediators were observed in the neonates. Inhibition of NFB activity in the neonates decreased apoptosis, but heightened inflammation, with increased expression of the same inflammatory genes elevated in the adults. In contrast, inhibition of NFB in the adults resulted in partial suppression of the inflammatory response. Conclusions: NFB activation in the neonatal lung is anti-inflammatory; protecting against LPS-mediated lung inflammation by repressing similar inflammatory genes induced in the adult.