OBJECTIVE: To assess the influence of socioeconomic background on malocclusion prevalence in primary dentition in a population from the Brazilian Amazon. METHODS: This cross-sectional study comprised 652 children (males and females) aged between 3 to 6 years old. Subjects were enrolled in private preschools (higher socioeconomic status - HSS, n = 312) or public preschools (lower socioeconomic status - LSS, n = 340) in Belém, Pará, Brazil. Chi-square and binomial statistics were used to assess differences between both socioeconomic groups, with significance level set at P < 0.05. RESULTS: A high prevalence of malocclusion (81.44%) was found in the sample. LSS females exhibited significantly lower prevalence (72.1%) in comparison to HSS females (84.7%), particularly with regard to Class II (P < 0.0001), posterior crossbite (P = 0.006), increased overbite (P = 0.005) and overjet (P < 0.0001). Overall, malocclusion prevalence was similar between HSS and LSS male children (P = 0.36). Early loss of primary teeth was significantly more prevalent in the LSS group (20.9%) in comparison to children in the HSS group (0.9%), for both males and females (P < 0.0001). CONCLUSION: Socioeconomic background influences the occurrence of malocclusion in the primary dentition. In the largest metropolitan area of the Amazon, one in every five LSS children has lost at least one primary tooth before the age of seven.