Objective To study the telomerase reverse transcriptase (TERT) mutation and the p53 pathway in T1 urinary bladder cancer (UBC). Materials and Methods This prospectively performed population-based study included all patients in the Southeast Healthcare Region in Sweden with T1 UBC registered in the period 1992-2001, inclusive. Given that p53 and TERT are important factors for tumour proliferation, although their interrelationships are unknown, we assessed both the TERT and the p53 mutations. Furthermore, we conducted a p53 immunohistochemistry (IHC) analysis using two thresholds for p53 positivity: 10% of tumour cells and 50% of tumour cells (p53 IHC50%). Cox proportional hazards analysis and Kaplan-Meier curves were used to study time to tumour progression. Results Out of 158 patients, we observed the TERT mutation in 74 (47%), the p53 mutation in 48 (30%), and p53 IHC50% positivity in 72 patients (46%). The TERT mutation was more common in p53 mutation-positive patients (P = 0.009), and the latter group also had more patients with p53 IHC50%-positive tumour cells (P = 0.02). In the TERT mutation-negative tumours a p53-positive mutation was associated with a shorter time to progression (P = 0.03) compared to patients with p53-negative mutation. In contrast, in tumours with both TERT mutation positivity and p53 mutation positivity, a longer time to progression was observed in the group with p53 IHC50% positivity compared to the group with p53 IHC50%-negative tumours. Conclusions In stage T1 UBC, the combination of the TERT mutation and the p53 mutation was associated with tumour progression. A protective effect of the TERT promotor mutation against tumour progression induced by the p53 mutation and subsequent p53 accumulation in tumour cells might be possible, but further investigations are necessary.