- A young psychiatric patient presented with a purulent collection in the lower abdominal wall. Simple drainage failed to heal the abdominal wall abscess, and the presence of a primary septic focus was suspected. Full investigation showed a right renal pelvis calculus with xanthogranulomatous pyelonephritis complicated by a retroperitoneal abscess. Recovery was complete after a nephrectomy. A review of the published literature demonstrated the rarity of this presentation, although even more curious cases have been described, including a urinobronchial fistula, as well as catastrophic cases presenting with a massive haemorrhage. Authors are unanimous that ultrasonography should be the first examination, the scanner being also of primordial value for the diagnosis and demonstration of the retroperitoneal spaces ans fascia. Treatment requires both rapid and radical surgical intervention.