Aim: We aimed to review the evidence of reducing the dose or number of BCG instillations in non-muscle invasive bladder cancer (NMIBC) patients. Material & methods: A literature search was done according to Preferred Reporting Items for Meta-Analyses statement. Results: Overall, 15 and 13 studies were eligible for qualitative and quantitative synthesis, respectively. In patients with NMIBC, lowering either the dose or number of BCG instillations increases the risk of recurrence, but not the risk of progression. Lowering the dose of BCG decreases the risk of adverse events compared with standard-dose BCG. Conclusion: Standard-dose and -number of BCG is preferred for NMIBC patients based on oncologic efficacy; however, low-dose BCG could be considered in selected patients who suffer from significant adverse events.