(1) Local and regional adverse effects (ulceration, abscesses and adenitis are generally mild, although they can persist for more than three months. Systemic effects are rare but potentially life-threatening (osteitis, disseminated BCG infection, anaphylaxis, etc.). (2) Some risk factors are related to the vaccine itself or to its administration (intradermal route, certain strains of vaccine, high doses, etc.). There are very few data on the adverse effects of multipuncture BCG administration. (3) The frequency of adverse effects is inversely related to age at vaccination. The vaccine can cause severe disseminated BCG infection, especially in subjects with congenital or acquired immunodeficiency (notably HIV infection and immunosuppressive therapy). (4) The risk of adverse effects can be minimised by avoiding patients with contraindications and by careful administration.