Objective: To investigate the diagnosis and treatment of hydronephrosis caused by retroperitoneal fibrosis.Methods: A retrospective study from 1998 up to 2008,for the diagnosis and treatment of 5 cases of hydronephrosis caused by retroperitoneal fibrosis was made.Results: One patient secondary to malignancy died in 3 months after operation.The other patients were followed up for 3 to 48 months with the involved kidneys normal in size and shape.Conclusion: Retroperitoneal fibrosis should be considered in hydronephrosis without agent.B mode ultrasonography,CT,MRI and retrograde urogram are very important in the diagnosis.Drug therapy is only used in the early stage of RPF,while surgical therapy should be resorted for advanced disease.