The ultrasonic findings of three patients with surgically confirmed xanthogranulomatous pyelonephritis are presented. All of the involved kidneys were markedly enlarged, had a large central echogenic area, and demonstrated an increased parenchymal anechoic pattern. The appearance correlated well with the other radiographic and gross pathologic findings. While this appearance was fairly distinctive, it is anticipated that there will be some difficulty in distinguishing this entity from simple hydronephorsis, especially in conjunction with staghorn calculus. It is also anticipated that focal xanthogranulomatous pyelonephritis will have an atypical appearance.