I am going to assume you mean retroperitoneal fibrosis. It is disorder caused by an aggregation of cells (fibrous mass) in the back of the abdomen, which may block the tubes that carry urine from the kidneys to the bladder (ureters).
It also goes by other names such as Idiopathic retroperitoneal fibrosis; Ormond's disease.
Retroperitoneal fibrosis is caused by the proliferation (growth) of fibrous tissue in the retroperitoneum (the area of the body behind the stomach). Physicians don't know why these masses form. The disorder is rare, usually affecting people age 40 to 60, and men are twice as likely to be affected as women. The symptoms are caused by the obstruction of the ureters.
Hope this helps you out some.
[This message has been edited by moderator1 (edited 12-04-2002).]