A 76-year-old woman presented with spiking fever and right back pain. Ultrasonography (US) revealed that her right kidney was enlarged. Computed tomography (CT) showed the parenchyma was replaced by non-enhancing masses but the overall kidney shape was maintained. These findings were compatible with those of xanthogranulomatous pyelonephritis (XP). The nonenhancing masses on CT coincided with the multiple butter yellow nodules of the resected kidney and microscopically these lesions were proved to be abscesses with xanthoma cells. In this case, the US and CT findings reflected the pathological feature of XP and thus these techniques are thought to be useful for the diagnosis of XP.(Internal Medicine 36: 586-590, 1997)