Based on retrospective analysis of 430 cases of retroperitoneal fibrosis, a classification into various etiological groups and an evaluation of the best diagnostic approach and treatment was possible. In patients presenting moderate upper urinary dilation corticosteroids alone proved to be of value in 93% of cases. Azathioprin given in combination with corticosteroids seems to be effective. The surgical 'therapy of choice' was ureterolysis with an effective intraperitoneal transposition. Ureteral restenosis after this procedure (in 22%) occurred mainly when it was not combined with long-term corticosteroid therapy. When the lower half of the ureter is involved we favor ureterolysis, its prevesical section, complete intraperitoneal transposition and a primary psoas-hitch bladder flap.