Résumé : We report the case of a 24-year old man with a past history of vesical extrophy and ureterosigmoidostomy in childhood, admitted with acute left flank pain and acute renal failure. The complaints started the day following the endoscopic resection of a sigmoid polyp. The stricture of the ureterosigmoid junction was diagnosed by intravenous urography. Conservative treatment with endo-ureteral dilatation was successfully performed. At 2 years of follow-up, the patient is still asymptomatic, without any residual hydronephrosis.