Bacillus Calmette-Guérin (BCG) immunotherapy represents a valuable treatment in the management of superficial bladder cancer, but the therapy is not without its risks. A total of 220 patients have been included in a review of local and systemic side effects associated with BCG immunotherapy. The majority of side effects are mild and self limiting, but potentially life threatening complications can arise with BCG immunotherapy. These systemic side effects include pneumonitis/hepatitis and systemic BCG infection. Recommendations are given for the use and administration of BCG, and if these rules are correctly applied, BCG may be administered safely, and with confidence.