Idiopathic retroperitoneal fibrosis (IRF) may cause ureteric obstruction with renal damage. Ureterolysis with intraperitonealization of the ureter is commonly used as primary treatment. We gave corticosteroids for two years to six patients, four males and two females, between 40 and 56 years of age. one of the patients is in his tenth month of treatment and another in the fourth month. Between 4 and 74 months (mean 40.4 months) after initiation of treatment, kidney function had improved, or was preserved in previously functioning renal units, and the patients were free from symptoms. We conclude that steroids may be used as primary treatment of IRF after histological or cytological diagnosis to exclude retroperitoneal malignancy. Steroids should also be part of the treatment strategy in patients with a more aggressive disease who may need surgery. Patients with IRF should be followed for the rest of their lives after discontinuation of steroid therapy.