This study analyzed socio-spatial inequalities in the adequacy of Ministry of Health data systems on live births (SINASC) and deaths (SIM) for estimating infant mortality at the municipal level in Brazil. Data from 2000-2002 for all municipalities were analyzed according to population size and geographic region. Five indicators were considered: age-standardized mortality rate; ratio of reported-to-estimated live births; relative mean deviation of the mortality rate; relative mean deviation of the birth rate; and proportion of deaths with undetermined causes. Adequacy criteria were established statistically for eight Brazilian States in which vital statistics were adequate. The results showed important socio-spatial inequalities: in general, the proportion of adequate vital statistics was higher in the Central-South of the country and in larger municipalities. The live birth data system received the best evaluation for three items. The mortality data system requires both a reduction in underreporting and improved data on cause of death in order to orient health programs focused on decreasing inequalities in infant mortality in Brazil.