Of 23 cases of surgically proven retroperitoneal fibrosis evaluated by computed tomography (CT), 11 were examined preoperatively, while 12 were examined by CT in a retrospective study. The fibrosis appeared as a prevertebral retroperitoneal mass or as a fibrous sheet covering the central vessels and the ureters in 15 patients. The CT appearance corresponded well with the surgical findings in these cases. CT failed to visualize the fibrosis in eight cases mainly when the fibrosis was limited to the pelvis surrounding the distal ureters. A combination of retroperitoneal fibrosis and aortic aneurysm was found in five cases. CT is considered valuable in the evaluation of patients wtih suspected retroperitoneal fibrosis. It gives direct information about the fibrosis and is usable also in uremic patients.