The Armando Ribeiro Gonçalves Dam, popularly known as The Açu Dam, is an important geotechnical construction in Rio Grande do Norte state, Northeastern of Brazil. The monitoring and analysis of strains in earth dams is essential to understanding the safety conditions of these structures. The present study aimed at analyzing vertical strains at the Açu Dam using data from instruments installed in the body of the dam, and numerical modeling, in order to compare the results. The study was conducted in the construction stages of the embankment of the dam, first filling and reservoir operation. Numerical analyses were conducted with Sigma/W software, which uses the finite elements method to analyze stress and strains. The results of modeling were compared to instrumentation data reported in Rocha(Barragem Engenheiro Armando Ribeiro Gonçalves: histórico e avaliação do comportamento atual, Universidade Federal do Rio Grande do Norte, Natal, 2003). Analyzing the results of the instrumentation, it was found that the largest settlement measured was 39.71 cm, corresponding to 0.63% of the total height of the dam, and that the settlement occurred mainly in the construction period and upstream. Comparing the results between modeling and instrumentation, a good agreement is observed, especially during the construction period, mainly for the extensometers located downstream, with relative errors between 0.53% and 5.89%. It is concluded that the modeling performed and the parameters of the soils used corresponded well to the reality of the Açu dam, resulting in a satisfactory stress–strain analysis.