Computed tomography (CT) scan was performed within 6 h in 91 patients with minor head injury (MHI). Eight patients (9%) demonstrated intracranial lesions on CT scan (6 brain contusions, 1 brain edema and 1 extradural hematoma). No patient required craniotomy. In patients with normal CT scan, no complications to the head injury were observed. Patients with intracranial lesions were hospitalized significantly longer (mean 9.4 days) than patients without (mean 1.6 days). In a subgroup of 50 patients with normal CT scan, serum S-100 protein was measured on admission. Elevated S-100 levels were seen in 10 of 50 patients (0.5-2.4 mug/L, mean 1.1). These patients were hospitalized significantly longer (mean 3.4 days) compared to patients with normal CT scan and normal S-100 levels (mean 1.1 days). MHI patients with GCS 14-15 without neurological deficits can safely be discharged when CT scan is normal. Serum protein S-100 measurements appear to provide information about diffuse brain injury after MHI.