Bacille Calmette-Guérin (BCG) has been used by urologists intravesically for the treatment of bladder cancer for several years after its first reported use as a cancer therapy in the 1930s. The treatment regimen that still exists today was described by Morales in 1976 with the usage of BCG as a once weekly intravesical instillation for six weeks. In this review article, intravesical BCG efficacy mechanisms, dose, strains and clinical recommendations were discussed with the help of current literature. The mechanisms by which BCG exerts its anti-tumour activity is still unclear. Attachment to the bladder via fibronectin and stimulation of killer cells, T lymphocytes and monocytes were supposed to provide anti-tumour activity. Although factors of BCG failure remain largely unpredictable, maintenance BCG is currently the most effective intravesical agent. It has been proved that tumour recurrence and risk of progression in high risk patients were significantly reduced. The primary treatment for carcinoma in situ is intravesical BCG. In near future, new studies with antifibrinolytic agents and nanoparticles may play an important role in order to increase BCG efficacy.