This paper provides recommendations on the management of complications arising from intravesical treatment with bacillus Calmette–Guérin (BCG) for nonmuscle-invasive bladder tumors. There is minimal recommendations currently available as randomized trials on the side effects of intravesical BCG are lacking and severe complications are usually described in case reports only. All physicians giving intravesical BCG should be aware of the possible complications that could arise and how to treat these. The incidence of bladder irritation, general malaise, and fever is very high, while severe complications remain rare. Approximately 8% of patients have to stop treatment because of these complications. BCG infections and reactions can occur anywhere in the body, and may happen straight away or even several months or years after BCG treatment, making early diagnosis difficult. Additionally, correct diagnosis is hampered by the uncertain appearance of BCG in tissue and body fluid. An essential step in the management complications arising from BCG is written information for both the family doctor and the patient on the possible adverse events and their management. Recent data demonstrated that none of the earlier advocated methods to prevent BCG toxicity are valid: lowering the dose, tuberculostatic drugs, or oxybutynin. Severe complications are treated with three or four tuberculostatics over 3–12 months, depending on the severity of the situation. Corticosteroids are an essential therapy in BCG septicemia. Nonsteroidal anti-inflammatory drugs and corticosteroids can manage efficiently the immunological complications.