Retroperitoneal Fibrosis is not contagious. It is a rare condition characterized by the formation of fibrous tissue in the retroperitoneal space, which surrounds the abdominal organs. It is not caused by an infection or transmitted from person to person. The exact cause of this condition is still unknown, but it is believed to involve an abnormal immune response. Retroperitoneal Fibrosis typically affects adults and can lead to various symptoms and complications if left untreated.