Xanthogranulomatous Pyelonephritis(XP) is a rare, chronic bacterial infection(E.Coli) of the kidneys characterized by diffuse renal destruction. The condition often co-exists with obstructive uropathy secondary to nephrolithiasis. The kidney is usually non-functioning and enlarged and case reports involving surrounding organs have been described. It is also known as an ‘inflammatory tumor’ and is known to mimic malignancy radiologically and histologically. XP is more common in females in ratio of 4:1, usually noted in the 4th to 5th decades of life and is generally unilateral, more frequently involving the right kidney. It has been described in three stages: 1) Kidney alone 2) Kidney and perinephric fat, and 3) Kidney, perinephric fat and retroperitoneum extension Clinical Presentation: In a case series report involving fifteen cases, the most common presenting symptoms and signs were: Loin pain (86.6%) Renal angle tenderness (73.3%) Palpable lump (46.6%)-Secondary to hydronephrosis/pyonephrosis Pyrexia and Burning micturation (25%) Associated conditions: Non-functioning kidney (93.3%) Renal Calculi in pelvis (66.6%) Fistulae Important differentials include: Malignancy: Clincial features, radiology, histology will show foam cells in XP Chronic Pyelonephritis with calculi Renal Tuberculosis Perinephric Abscess Radiological Features and Management: CT scan with contrast is the most accurate imaging technique for evaluating the disease and extrarenal spread. Key radiological features: Before the introduction of computed tomography (CT) and ultrasound (US), the correct preoperative diagnosis was rarely made. Although the focal form may still be mistaken for a renal cell carcinoma, the more commonly seen diffuse process has characteristic imaging features. Ultrasound demonstrates renal enlargement with multiple anechoic or hypoechoic masses replacing the normal corticomedullary differentiation and a contracted pelvis. CT Scan • Presence of calculi • Increase in renal volume • Hydronephrosis • Hypodense areas with density measurements from 15 to 25 HU (due to focal parenchymal destruction filled w/pus and debris) • Extrarenal involvement/presence of fistulas IVP • Nonfunctioning kidney • Calculi PET Scan • Multiple hypodense collections with low FDG uptake • Central photopenia and rim of hyperactivity Treatment is broad spectrum antibiotics and nephrectomy.