Live Birth Information System (SINASC) was decentralized in order to improve the use and the quality of the information, being the basis for service evaluation and epidemiological studies. This study evaluated the percentage of unfilled fields in the variables related to newborn, mother and delivery on Live Birth Certificates in 38 municipalities of Minas Gerais. Population was composed by the newborns of resident mothers, available at the database, between 1998 and 2005. The evaluation considered the population size and the healthcare management of studied municipalities. It was observed an improvement in the filling of Live Birth Certificates in the analyzed period in the studied municipalities. An important reduction on the percentage of unfilled fields was observed in the variables: race/color, literacy, civil state, number of live born sons and number of dead born sons. Live Birth Information System decentralization led to an improvement in the percentage of unfilled fields of certificates in the studied municipalities, regardless of population size and healthcare management.