Background Protein S100B has proven to be a useful biomarker for cerebral damage. The predictive ability of S100B may, however, be affected by extracerebral injuries. The aim of this study was to investigate serum levels of S100B in patients with either isolated head injury (IHI), multi trauma with head injury (MTHI), or no head injury (NHI). The primary aim was to assess if a significant difference in serum levels of S100B could be found between IHI and MTHI patients. Methods Patients (233) were primarily admitted to the trauma centre. Serum samples were drawn on admission and 6 h after trauma and then stored at -80°C until analysed. Variables included Abbreviated Injury Scale (AIS) for head trauma, Injury Severity Score (ISS) and 30-day survival. Results Two patients could not be classified. IHI occurred in 28, MTHI in 102 and NHI was found in 101. The median S100B concentrations on arrival were 0.47, 1.68 and 0.49 µg/l, respectively (p