Background: Hotspot mutations in the promoter of the gene coding for telomerase reverse transcriptase (TERT) have been described and proposed to activate gene expression. Objectives: To investigate TERT mutation frequency, spectrum, association with expression and clinical outcome, and potential for detection of recurrences in urine in patients with urothelial bladder cancer (UBC). Design, setting, and participants: A set of 111 UBCs of different stages was used to assess TERT promoter mutations by Sanger sequencing and TERT messenger RNA (mRNA) expression by reverse transcription-quantitative polymerase chain reaction. The two most frequent mutations were investigated, using a SNaPshot assay, in an independent set of 184 non-muscle-invasive and 173 muscle-invasive UBC (median follow-up: 53 mo and 21 mo, respectively). Voided urine from patients with suspicion of incident UBC (n = 174), or under surveillance after diagnosis of non-muscle-invasive UBC (n = 194), was tested using a SNaPshot assay. Outcome measurements and statistical analysis: Association of mutation status with age, sex, tobacco, stage, grade, fibroblast growth factor receptor 3 (FGFR3) mutation, progression-free survival, disease-specific survival, and overall survival. Results and limitations: In the two series, 78 of 111 (70%) and 283 of 357 (79%) tumors harbored TERT mutations, C228T being the most frequent substitution (83% for both series). TERT mutations were not associated with clinical or pathologic parameters, but were more frequent among FGFR3 mutant tumors (p = 0.0002). There was no association between TERT mutations and mRNA expression (p = 0.3). Mutations were not associated with clinical outcome. In urine, TERT mutations had 90% specificity in subjects with hematuria but no bladder tumor, and 73% in recurrence-free UBC patients. The sensitivity was 62% in incident and 42% in recurrent UBC. A limitation of the study is its retrospective nature. Conclusions: Somatic TERT promoter mutations are an early, highly prevalent genetic event in UBC and are not associated with TERT mRNA levels or disease outcomes. A SNaPshot assay in urine may help to detect UBC recurrences. (C) 2013 European Association of Urology. Published by Elsevier B. V. All rights reserved.