The aim of this study is to evaluate the quality of socioeconomic and demographic information, for all Brazilian Federal Units (BFU), retrievable from the Brazilian Mortality Information System (aka SIM). The paper assesses SIM’s potentiality to monitor inequalities in the field of infant mortality. Accessibility, opportunity, methodological soundness, relevance, completeness, and consistency have been explored as quality indicators. The variables as follows were assessed: race, birth weight, gestational age, medical assistance, parity, maternal educational background, age, and occupation of the mother. SIM’s documents as well as the scientific literature on child mortality were revised. The proportions of data incompleteness, by region and BFU, were calculated, with the identification of factors that may influence (in)completeness using logistic regressions. In spite of the accessibility of the database and the relevance of most of its variables, SIM has serious quality problems, such as: confusing instruc tions in the information manual for missing data, misclassification of maternal occupation, absence of data on informants’ race/ethnical background, and high proportions of incomplete information. SIM does not seem to be a reliable source to monitor, evaluate, and plan actions aiming to minimize child health inequalities.