Of 428 biopsy specimens, the TERT C228T mutation was detected in 9% (31/364) of normal urothelium, 27% (4/15) of urothelial dysplasia (UD), 50% (9/18) of UD suspicious for carcinoma in situ (CIS), and 58% (18/31) of CIS. Here, TERT is linked to urothelial dysplasia.