Upper urinary tract inverted papillomas. 
Inverted papilloma is a rare, benign tumor.  Only 33 cases to date have been reported to have occurred in the upper urinary tract.  These lesions have a male predominance, are difficult to diagnose, and are associated with urothelial malignancy.  Because transitional cell carcinoma can present even 8 years after surgery and in other sites within the urinary system, careful follow-up is essential.  This article adds 2 new cases and 1 follow-up of a previously reported case from 1990.