PURPOSE: To assess the prevalence, lesion sites and characteristics of MR findings in patients with mild head injury and the relationship between MR findings and the postconcussion syndrome. MATERIALS AND METHODS: Our study involved 26 patients with mild head injury (Glasgow Coma Scale, 13 to 15 ; no subsequent deterioration ; loss ofconsciousness < 30 minutes). Prospective CT and MR Imaging was performed and the prevalence rate of abnormalities, sites and characteristics of lesions were evaluated, as well as the relationship between MR findings and the postconcussion syndrome. RESULTS: In 17 of 26 patients(65%) there were abnormal findings on MR, and in 8 of the 26(31%), abnormal findings were seen on CT. Abnormalities consisted of cerebral contusion in nine patients, diffuse axonal injury in six and small thin extracerebral hematomas in nine. MR is more sensitive than CT, especially when the lesion is non-hemorrhagic and is closer to the cranial vault. In 16 patients who wereclinically followed up, the prevalence rate of postconcussion syndrome was higher in those with abnormal MR than in those with normal MRI. CONCLUSION: The greater sensitivity of MR makes it a better indicator than CT for the presence and extent of injuries and thus potentially a better predictor of outcome, even in patients with mildhead injuries. Positive MR findings are an objective predictors for the evaluation of patients with postconcussion syndrome after mild head injury.