The sonographic and computed tomographic findings in 3 cases of diffuse xanthogranulomatous pyelonephritis are presented along with correlation with the pathological specimens. The combination of the findings in sonography and computed tomography in this condition enables one to make an accurate preoperative diagnosis. Calyces containing pus and/or xanthomatous tissue produced low-level echoes simulating preservation or thickening of the renal parenchyma on sonography. On CT the central low attenuation areas either gave negative values representing abundant xanthomatous tissue seen on gross pathology, or measured in the water density range representing a combination of pus and less abundant xanthomatous tissue.