Abstract: Objective: To explore the reasons of residual of pituitary adenoma after trans-sphenoid operation and to improve the effect of treatment. Methods: Retrospectively analysis 0f 118 consecutive cases of MRI convinced residual pituitary adenoma after trans-sphenoid operation both in our hospital and in other hospitals from October 1992 to January 2003. Results: The majority of the residual tumor tissue are located in cavernous sinus（CS）（46.6%）,sella tursica （37.3 %）,supra sella （5.1%）,mixed（8.3%） and extra-cranial （1.7%）;The main reasons that hinder radical removal are tumor involve cavernous sinus（46.6%）,less experience operator （36.4%）,tumor invasively growing （9.3%）,huge tumor （3.4%）and heavy bleeding （4.2%）.Treatment for the residual tumor includes re-operation 10.1%,linear accelerator-radiation treatment 39.0%,г-knife 38.2%,medication treatment 11.0%. Conclusion: The main reasons of residual for pituitary adenoma after trans-sphenoid operation is tumor involving cavernous sinus. These tumors can not or are very difficult to be radically removed simply by operation. The second reason is less experience and technical problem. Over half of the residual tumors could be totally or sub-totally removed through improved technique.