Abstract The objectives of this prospective, longitudinal, population-based study were to estimate the incidence of dental caries in the primary dentition, identify risk factors and determine the proportion of children receiving dental treatment, through a two-year follow up. The first dental exam was conducted with 381 children aged one to five years, at health centers during immunization campaigns; 184 of them had dental caries and 197 had no caries experience. The second exam was carried out two years later at a nursery or at home with the same individuals who participated in the first exam. The diagnosis of dental caries was performed using the dmft criteria. Parents were interviewed regarding socioeconomic indicators. Descriptive, bivariate and adjusted Poisson regression analyses were performed. Among the 381 children, 234 were reexamined after two years (non-exposed: 139; exposed: 95). The overall incidence of dental caries was 46.6%. The greatest incidence of dental caries was found in the group of children with previous caries experience (61.1%). Among the children without dental caries in the first exam, 36.7% exhibited caries in the second exam. The majority of children (72.6%) received no treatment for carious lesions in the two-year interval between examinations. Children with previous dental caries (RR: 1.52, 95%CI: 1.12-2.05) had a greater risk of developing new lesions, compared with the children without previous dental caries. The incidence of dental caries was high and most of children's caries were untreated. Previous caries experience is a risk factor for developing new carious lesions in children.