Introduction: Bacterial infection in a hydronephrotic kidney is referred to as infected hydronephrosis. In advanced cases, there is suppurative destruction of the renal parenchyma with a total or near total loss of renal function - a condition referred to as pyonephrosis. The kidney is transformed into a sac like structure filled with necrotic debris and purulent material. Presentation: The patient is usually quite ill with high-grade fever, chills, flank pain, and tenderness. A previous history of urinary tract infection, calculi, or surgery is commonly present. Ultrasound will show dilated pyelocalyceal system with fluid debris levels. Treatment: The diagnosis of pyonephrosis requires immediate drainage of the infected pelvis and appropriate antimicrobial therapy. The kidney can be drained via ureteral catheter. If this is not possible due to obstruction, a percutaneous nephrostomy tube can be placed. Once the pus has been drained, the underlying cause of infection can be dealt with. If the kidney is non-functioning or is severely infected (as in the case shown here), nephrectomy may be the only option. Case History: This nephrectomy specimen is from a 65 y/o male who presented with frequency and burning of micturition and tenderness in the right lumbar region. Urine examination showed turbid urine with proteinuria and numerous neutrophils (pyuria). Urine culture was positive for E. coli. Imaging studies showed severely hydronephrotic kidney, hydroureter and multiple ureter calculi. The specimen shows a 21 x 18 x 16 cm size kidney with markedly dilated pelvicalyceal system and paper-thin renal cortex. About 3 liters of thick, creamy yellowish pus was removed from the specimen. Microscopic examination of the thinned walls showed xanthogranulomatous inflammation and end-stage renal disease secondary to obstructive uropathy and pyonephrosis. Case courtesy of: Dr. Sanjay D. Deshmukh (Prof. of Pathology) & Dr. J. M. Gadekar (Head of Surgery Dept.), Dr. Vithalrao Vikhe Patil Medical College & Hospitals, Ahmednagar, India.