OBJECTIVE To discuss the clinical criteria for diagnosing diffuse axonal injury (DAI). METHODS Clinical and computed tomographic features of 117 patients with severe closed head injury were analyzed. The authors preliminarily put forward CT diagnostic criteria of DAI, that is, 1) single or multiple small intraparenchymal hemorrhages in the cerebral hemispheres (< 2 cm in diameter); 2) intraventricular hemorrhage; 3) hemorrhage in the corpus callosum; 4) small focal areas of hemorrhage adjacent to the third ventricle (< 2 cm in diameter); and 5) brain stem hemorrhage. All patients were divided into two groups, DAI and non-DAI group, according to the criteria. There were 42 patients in the DAI group and 75 patients in the non-DAI group. The injury causes, Glasgow coma scale (GCS) scores on admission, coexisting injuries and outcomes were compared between the two groups. The relationship between DAI and the outcomes in the patients with severe head injury was analyzed. RESULTS Traffic accident was the main injury cause in the cases of DAI. GCS scores on admission in patients with DAI were significantly lower than those in patients without DAI. The incidence of diffuse brain swelling (DBS) in the DAI group was significantly higher than that in the non-DAI group, whereas the incidences of both skull fracture and epidural hematoma (EDH) in the DAI group were significantly lower than those in non-DAI group. There was no significant difference between the incidence of subarachnoid hemorrhage (SAH) and subdural hematoma (SDH) in the two groups. The incidence of poor outcome in the DAI group was significantly higher than that in the non-DAI group, although there was no significant difference between the mortalities in the two groups. CONCLUSIONS Because DAI is a very important factor worsening the outcome of patients with head injury, it is essential to make a diagnosis as soon as possible. The clinical manifestations of DAI, however, are not specific and DAI does not show directly on CT scans, so it is difficult to make a definite diagnosis. The CT diagnostic criteria of DAI put forward in this article are practicable, though they are by no means perfect.