We report a case of idiopathic retroperitoneal fibrosis and rapidly progressive glomerulonephritis with serum antiproteinase 3 antineutrophil cytoplasmic antibodies (anti-PR3-ANCA), without clinical or histological signs of Wegener's granulomatosis, in a 46-year-old man. Our case and previously reported cases showing the same association support the hypothesis that the association is not fortuitous, but reflects a common immunological mechanism.