A Phase III clinical trial has been started in Japan to determine the optimal treatment strategy for patients with high-grade pT1 bladder cancer who have pT0 histology after second transurethral resection. The aim of this trial is to demonstrate the non-inferiority of relapse-free survival (excluding Tis or Ta intravesical recurrence) for watchful waiting compared with intravesical bacillus CalmetteGurin therapy for pT0 after second transurethral resection. Patients with high-grade pT1 bladder cancer at the first registration and pT0 after second transurethral resection at the second registration are randomized to either a watchful waiting arm or an intravesical bacillus CalmetteGurin therapy arm. A total of 575 patients at the first registration and 260 patients at the second registration will be accrued for this study from 38 institutions over 5 years. The primary endpoint is relapse-free survival (excluding Tis or Ta intravesical recurrence), and the secondary endpoints are overall survival, metastasis-free survival with bladder preserved, annual proportion of intravesical relapse-free survival, annual proportion of T2 or deeper relapse-free survival, adverse events and serious adverse events.