ObjectiveTo describe normal serum levels of S-100&bgr; in healthy children and determine whether serum S-100&bgr; levels after traumatic brain injury are associated with outcome.DesignProspective cohort study.SettingUrban, tertiary care, children’s teaching hospital.PatientsA total of 136 healthy children and 27 children with traumatic brain injury.MethodsSerum S-100&bgr; levels were measured in 136 healthy children. A total of 27 children with traumatic brain injury had S-100&bgr; levels collected within 12 hrs of injury. Other indices of severity of injury measured were admission Glasgow Coma Scale score, and Pediatric Risk of Mortality score at 24 hrs (PRISM 24). Outcome was measured by the Pediatric Cerebral Performance Category (PCPC) score at hospital discharge and 6 months postinjury or at death.Measurements and Main ResultsS-100&bgr; levels in healthy children had a mean of 0.3 &mgr;g/L (90% confidence interval, 0.03–1.47) and inversely correlated with age, (r= −.32,p< .001). In children with traumatic brain injury, 6-month postinjury outcome inversely correlated with Glasgow Coma Scale score (r= −.47,p= .01) and correlated with PRISM 24 score (r= .83,p< .001) and S-100&bgr; levels (r= .75,p< .001). Six months postinjury, comparing good outcome (PCPC ≤ 3, n = 20) vs. poor outcome (PCPC ≥ 4, n = 7), median admission Glasgow Coma Scale scores were 8 (range, 3–15) and 3 (range, 3–7,p= .01), median PRISM 24 scores were 7 (range, 0–19) and 30 (range, 18–35,p< .001), and median S-100&bgr; levels were 0.85 &mgr;g/L (range, 0.08–4.8 &mgr;g/L) and 3.6 &mgr;g/L (range, 1.4–20 &mgr;g/L,p< .001), respectively. A serum S-100&bgr; level of ≥2.0 &mgr;g/L is associated with poor outcome, with a sensitivity of 86% and a specificity of 95%. The area under the receiver operating curve for S-100&bgr; was 0.94 (±0.05).ConclusionsSerum S-100&bgr; levels in healthy children have a moderate inverse correlation with age. After traumatic brain injury in children, the acute assessment of serum S-100&bgr; levels seems to be associated with outcome.