The factors affecting outcome were analyzed in 1,064 patients, 621 males and 443 females aged 10 to 104 years (mean 46 +/- 23 years), with mild head injury (Glasgow Coma Scale [GCS] score > or =14) but no neurological signs presenting within 6 hours after injury. Intracranial lesion was found in 4.7% (50/1,064), and 0.66% (7/1,064) required surgical treatment. The Japan Coma Scale (JCS) and GCS assessments were well correlated (r = 0.797). Multivariate analysis revealed significant correlations between computed tomography (CT) abnormality and age > or =60 years, male sex, JCS score > or =1, alcohol consumption, headache, nausea/vomiting, and transient loss of consciousness (LOC)/amnesia. Univariate analysis revealed that pedestrian in a motor vehicle accident, falling from height, and mechanisms of injuries except blows were correlated to intracranial injury. No significant correlations were found between craniofacial soft tissue injury and intracranial injury. Patients with occipital impact, nonfrontal impact, or skull fracture were more likely have intracranial lesions. Bleeding tendency was not correlated with CT abnormality. The following indications were proposed for CT: JCS score >0, presence of accessory symptoms (headache, nausea/vomiting, LOC/amnesia), and age > or =60 years. These criteria would reduce the frequency of CT by 29% (309/1,064). Applying these indications to subsequent patients with GCS scores 14-15, 114 of 168 patients required CT, and intracranial lesions were found in 13. Two refused CT. Fifty-four of the 168 patients did not need CT according to the indications, but 38 of the 54 patients actually underwent CT because of social reasons (n = 21) or patient request (n = 17). These indications for CT including JCS may be useful in the management of patients with mild head injury.