This study is a quantitative and qualitative assessment of data from the Brazilian Information System on Live Births (SINASC) in Brazil. Coverage of the data by municipality was estimated as the ratio between reported and estimated live births. Data quality in the SINASC was assessed via probabilistic linkage with the database from the Birth in Brazil study, 2011-2012, and kappa coefficients of agreement were calculated. In 2013, data coverage was high and homogeneous in all states of Brazil. However, the analysis according to municipalities (counties) showed greater spatial heterogeneity. As for completeness of information in SINASC, kappa coefficients were statistically different from zero for all the tested variables (p < 0.001), and marginal distributions of all the variables were similar in the two databases. Gestational age was the variable with the worst agreement, with a kappa value of 0.461. The indicator that describes the inconsistencies, measured by the sum of the square of the differences between the reported and expected prematurity rates by birthweight bracket, showed the highest value in the North of Brazil and the lowest in the South, pointing to geographic inequalities in measurement of gestational age.