To evaluate recurrence, progression, and cancer-specific mortality of high-grade T1 non-muscle-invasive bladder cancer by assessing receipt of a low dose of the underexplored bacillus Calmette-Guérin (BCG) Moreau strain in a retrospective observational cohort study. From January 2006 to December 2015, a total of 219 consecutive patients with high-grade T1 non-muscle-invasive bladder cancer received half-dose (40 mg; n=109) or standard-dose (80 mg; n= 110) BCG Moreau strain after transurethral resection of the bladder. BCG therapy was initiated 2 or 3 weeks after transurethral resection of the bladder using the following protocol: 6 weekly doses, 12 monthly, 4 once every 3 months, and 2 once every 6 months, with a total of 24 doses. Comparing the half-dose and standard-dose treatment groups, in a median follow-up of 74.6 months, recurrence (n= 51, 46.8% vs. n= 60, 54.5%, P= .28), progression (n= 18, 16.5% vs. n= 16, 14.5%, P= .69), and disease-specific mortality (n= 9, 8.3% vs. n= 5, 4.5%, P= .26) were not significantly different on Kaplan-Meier curves and log-rank test, respectively. Charlson comorbidity index was an independent predictor of death from disease (hazard ratio= 1.341; 95% confidence interval, 1.033-1.740; P= .0274); no predictor of recurrence or progression was identified. Treatment intolerance occurred in 1 (0.9%) versus 6 (5.4%) patients (P= .12), respectively. No hospital admission or systemic BCG toxicity was reported. To our knowledge, this is the largest low-dose Moreau BCG strain study in high-grade T1 scenario. A half dose of BCG Moreau strain might be safe and effective in terms of tumor control, progression, or cancer-specific mortality with a low complication rate, which is central to the worldwide scenario of BCG shortage, and can help regulatory agencies approve efficient daughter BCG strains.