The bacillus Calmette-Guérin (BCG) is the attenuated strain of Mycobacterium bovis used in developing countries for preventing serious forms of tuberculosis. The neonatal BCG vaccine is applied in countries with high prevalence of tuberculosis. Most of the vaccinated individuáis develop no adverse reactions; although, some subjects show side effects due to a host altered immunity. These reactions range from a simple adenomegaly in the same side of BCG vaccine inoculation, to a spread infection, often fatal. A regional or systemic spread has been described in patients with secondary or primary immunodeficiencies and partial or total genetic defects of interleukin IL-12/23 and IFN-γ called as a whole "Mendelian susceptibility to mycobacterial infections" (MSMD). We describe five patients infected with M. bovis BCG-diagnosed between 1995-2008, at the base hospital in the city of Puerto Montt, Región de Los Lagos, Chile. These patients have the clinical course of MSMD.