Abstract: Objective: To evaluate CT diagnosis and clinical application in external hydrocephalus(EH).Methods: The CT features of 63 cases of EH were retrospectively analyzed.The ratio of the transverse diameter of the ventricle and skull was measured in all the cases.Results: The characteristic CT features of EH were as follows:(1) Widening of the interhemispheric fissure,Widening of the subarachnoid space in the bifrontoparietal regions;(2) Widening and deepening of the sulcus in the bifrontoparietal regions in some cases,edge like petal;(3) Widening and enlargement of the cistern of bilateral fossae and suprasellae cistern in some cases;(4) little or slight enlargement of the cerebral ventricles and(5) The ratio VT/ST was smaller than 15%.Conclusion: Combining the characteristic CT features with the clinical findings such as enlargement of the head circumference,expansion of the anterior fontanel,seizures of convulsion,etc,a physician is diagnose EH.CT plays an important role in the diagnosis and management of the patients with EH.