Keratinizing squamous metaplasia of the renal pelvis is a rare lesion of the upper urinary tract that can occur in the context of chronic aggression to the urothelium, potentially leading to a secondary pyeloureteral junction syndrome. We report the case of a 43-year-old patient discovered intraoperatively in relation to a renal pelvis stone causing a pyeloureteral junction syndrome. The extemporaneous histological examination ruled out a malignant process, and we performed a pyeloplasty according to KUSS-ANDERSON technique. This pathology should be recognized by the urologist for appropriate management. Treatment is conservative, with extended follow-up to detect recurrences or carcinomatous degenerations.