Complications of bacille Calmette-Guérin (BCG) vaccination are uncommon. Fewer than one in 1000 people vaccinated develop significant local reactions, and serious disseminated disease develops in fewer than one in a million. Localised complications--which include hypersensitivity reactions, abscesses at the injection site, and localised lymphadenopathy--are usually self limiting. They usually result from faulty technique, including the accidental intracutaneous injection of the stronger percutaneous vaccine, or poor selection of subjects for vaccination. Abscesses at the injection site usually respond to drainage and chemotherapy with isoniazid or erythromycin. Lymphadenopathy responds poorly to antimicrobial treatment and surgery may be needed for suppurating or discharging lesions to hasten recovery and give a good cosmetic result. Disseminated disease usually occurs in people with impaired immunity, in whom it is often fatal. BCG should never be given to people who are known to be infected with HIV, but the risk of complications in children born to HIV infected mothers is low. Disseminated disease can also result from intravesical instillation of BCG to treat bladder cancer, but this responds to antituberculosis chemotherapy.