The World Health Organization (WHO) currently recommends BCG vaccination at birth in developing countries. Pre-term infants should be vaccinated when they reach the chronological age of 40 weeks. Due to difficulties in establishing the correct gestational age, the vaccination policy for BCG in many developing countries is defined by birth weight rather than by gestational maturity. In the study area, low birth weight (LBW) infants (< 2500 g) are not supposed to be vaccinated at birth; instead the mother is asked to return for vaccination when the child has gained sufficient weight. BCG has marked immune stimulatory effects in both animal and human studies and observational studies suggest that BCG is associated with a non-specific reduction in mortality in areas with high infant and child mortality. The specific objective of the study is to examine the effect of early vaccination of LBW children for adverse events, purified protein derivative of tuberculin (PPD) reaction, scar size, morbidity, and mortality in a randomised prospective study of BCG vaccination at birth versus later (according to policy) among children 19 months of age in Guinea-Bissau. The hypothesis is that BCG vaccination of low birth weight (LBW) children at birth reduces infant mortality of this high-risk group by 25%.