Serial abdominal computed tomography (CT) scans have been performed in 15 patients with biopsy-proven idiopathic retroperitoneal fibrosis. Twelve patients had abdominal CT both before diagnosis and at a variable time later. All 12 patients showed a decrease in the size of the retroperitoneal mass at follow-up, although two had not been treated with steroids. The remaining three patients who had abdominal CT at some stage after diagnosis all showed a small residual retroperitoneal mass. Based on the findings, guidelines for the use of CT in the follow-up of retroperitoneal fibrosis are discussed.