The serum concentration of S-100B is reported to reflect the severity of brain damage. The purpose of this study was to determine whether elevated serum S-100B concentrations were related to neuropsychological test performance of patients in the subacute phase of recovery from mild traumatic brain injury (TBI). S-100B concentrations were measured in blood samples taken within 6 h after TBI. Serum S-100B was estimated using an immunoluminometric assay. Cognitive speed and memory were assessed with neuropsychological tests at a median of 13 days (range 7-21 days) after injury. The two groups, formed on a median split of initial serum S-100B concentrations (>or<0.22 microg/l) did not differ in age or education. The neuropsychological performance of the TBI patients was also compared with that of a healthy control group. Cognitive speed and memory performance of mild TBI patients were inferior compared to those of healthy subjects. There were no significant differences within the TBI group when serum S-100B concentration was taken into consideration. The findings suggest that serum S-100B levels after mild TBI are not predictive of neuropsychological performance in the subacute stage of recovery. Copyright (c) 2005 S. Karger AG, Basel.