A total of 481 cases of retroperitoneal fibrosis (RPF) presented in the literature have been reviewed. Ten additional cases from this hospital have been added. One etiological factor, methysergide, has been implicated in 12.4 percent of cases, but the majority remain unexplained. Characteristically, the patient will be male (2:1 ratio), in his 50's (30.9 percent), with vague lower back pain (34.2 percent) or possibly flank pain (34.0 percent). Physical examination usually will be unrevealing. The patient's serum chemistry probably will show some degree of azotemia (55.4 percent) and perhaps anemia (13.6 percent). The intravenous pyelogram characteristically shows bilateral hydroureteronephrosis (67.6 percent) or unilateral hydroureteronephrosis (20.3 percent) associated with medial deviation of the ureter due apparently to external compression of the ureter. Methysergide should be discontinued if implicated. Laparotomy for ureteral compression characteristically will reveal a dense, rubbery plaque in the retroperitoneum. Generous frozen section biopsies show fibrosis, usually with some chronic inflammation, suggestive of RPF. Careful inspection of retroperitoneal nodes and liver may reveal the presence of malignancy in 7.9 percent of patients. In the absence of malignancy, the ureters should lyse fairly freely and peristasis may return. If no malignancy is present on permanent sections of biopsy material, the patient can be given a fairly optimistic prognosis (cumulative mortality rate, 9 percent). Suboptimal improvement probably is an indication for steroid therapy and surgical re-exploration may become indicated. In these cases further search for malignancy should be undertaken.