SummaryIn September 1969 a 46 year-old patient was hospitalised for pain in the right lumbar region and right hypochondrium of five months duration. Urineanalysis revealed leucocyturia and aerobacter was grown on culture. Except for a high ESR, laboratory examinations were unremarkable An IVP showed a normal left kidney, and a stag-horn calculus in an afunctional right kidney. On retrograde pyelography the right pelvis could not be filled. As a tumor could not be excluded, lumbotomy was performed. The surgical diagnosis was inoperable tumor. A biopsy revealed xanthogranulomatous pyelonephritis.The patient did not show up until May 1972 when she was seen in uremic coma, for which she was treated conservatively. A staghorn calculus with moderate hydronephrosis had appeared on the left side and renal function had clearly deteriorated (23 ml./min.).In the following months two peritoneal dialysies were necessary. When seen lastly creatinin levels of 6.25 % were observed.Xanthogranulomatous pyelonephritis seems to be more frequent in women (sex ratio 2.35 women/I man), occurs at any age (2 months–82 years). The real incidence of the disease is unknown, so as the etiology. Suggestive for the diagnosis are recurrent urinary tract infections in a female patient, with on IVP calculi in a gross afunctional kidney. Bilateral disease is rare. Angiography is of no help in the differential diagnosis and the therapy should be nefrectomy, if possible.