A 25-year-old Nigerian black woman was found to have polyps involving the rectum, rectosigmoid, and sigmoid colon on air-contrast barium-enema examination. Resection of a segment of sigmoid colon revealed numerous polyps that were predominantly of the juvenile type, in keeping with the diagnosis of juvenile polyposis of the colon. This case is unusual because of the coexistence of retroperitoneal fibrosis with juvenile polyposis of the colon. In addition, one of the colonic polyps was a villous adenoma. The implications of these findings are discussed in relation to polyposis syndromes reported previously.