This paper aimed to evaluate the relationship between the lack of filling in education level information of adult deaths in the Brazilian Mortality Information System (SIM, by its Portuguese acronym) with sociodemographic characteristics of the deceased. Using sociodemographic information from SIM, a descriptive temporal analysis of the percentages of missing data in the education variable was performed. Next, the relationship between the lack of completion for education information was evaluated with sociodemographic variables. It was observed that men, at older ages, white, widowed, who died on public roads and due to external causes have a greater chance for failure in filling out the education information. Furthermore, it was found that the chance of presenting missing data is lower in the northern region compared to the other regions. It is generally concluded that the distribution of failure to complete the education information for deaths registered in the SIM is not uniform across spatial, socioeconomic and demographic characteristics.