Study design: Cases studies and review of patients with occult tethered cord syndrome(OTCS).Objective: To describe the MR features and mechanism of occult tethered cord syndrome.Methods: 17 patients were been studied.11 patients were symptomatic TCS without abnormality in MRI, 6 patients had the same MRI features as TCS without any TCS clinical symptoms.The clinical and radiology diagnostic was made by the surgeons and radiologists respectively according to related standard.The characteristics of both clinical and MRI features was identified in contrast with surgical results.Results: 11 of 17 cases showed normally eonus medullaris and terminal filum position with voiding dysfunction, lower-extremity weakness, pain and gait disturbance.These patients showed other MR findings which were not regarded as TCS diagnosis.These findings included anterior or posterior displacement of spinal cord and filum (5 cases), decrease diameter of conus medullaris (6 cases).8 of 11 patients were post-operation cases of spinal canal.6of 17 patients were be observed to have no clinical symptoms except bedwetting experience in routine life in 3 patients.MR findings of these 6 patients showed typical feature of TCS.Conclusion: Occult tethered of spinal cord may be regarded as secondary tethered of cord or another type of TCS.MR findings of these patients may be normal, abnormal or atypical abnormal.Clinical Symptoms should be the golden standard of diagnosis on these patients.The causes maybe trauma, subarachnoid space obstructed by adhesion after operation and tumors developed in the spinal canal or spinal cord which resulted in spinal cord isehemia without abnormality anatomy changes.The accurate mechanism of some OTCS remains unknown.