bjectives To determine whether a half-dose of bacille Calmette–Guérin (BCG) can reduce toxicity without affecting its efficacy in the management of non-muscle-invasive bladder cancer. Patients and methods From January 2012 to January 2014, 80 patients with superficial bladder cancer and in the intermediate-risk group were simply randomised to receive two different doses of BCG, i.e., a full dose of 90 mg (group A) or a half-dose of 45 mg (group B). There were no significant differences in clinical and pathological characteristics between the groups. At completion of the study, 40 patients could be evaluated in each group. Results All patients were evaluated for a follow-up of 12 months after treatment. There was no significant difference in recurrence rate (15 patients, 38%, in group A and 16, 40%, in group B) in the two groups, and no difference in progression rate of the disease, at eight patients (20%) in each group. There were significant differences between groups A and B in toxicity (grade 1 adverse events, 70% vs. 60%; grade 2, 18% vs. 7.5%, respectively). Grade 3 adverse events were only reported in group A (2.5%). Conclusion The half dose of intravesical BCG instillation can reduce the toxicity and side-effects that are associated with the treatment of superficial bladder cancer, without affecting the efficacy of therapy.