Abstract The aim of this study was to investigate the prevalence of unsatisfactory dental restorations on posterior primary teeth and associated factors in school children aged six to ten years. A cross-sectional study was conducted with children randomly selected from public schools in a small Brazilian town. Questionnaires were sent to the guardians addressing socioeconomic and behavioral aspects of the child. Oral examinations were performed at the schools to determine the quality of dental restorations, visible biofilm, and presence of moderate/extensive untreated caries (scores 3-6 ICDAS). This examination was performed by two previously trained and calibrated examiners. Associations were tested using multilevel logistic regression. Among the 400 children evaluated, 98 had restorations (217 teeth). The prevalence of unsatisfactory restorations was 34.6%. Restorations in amalgam were less likely to fail compared to those in glass ionomer cement (OR = 0.11; 95%CI: 0.02–0.49; p = 0.005). Children with moderate/extensive untreated caries were more likely to have unsatisfactory restorations (OR = 6.79; 95%CI: 2.20–20.93; p = 0.001). Children with a visible plaque index ≥ 20% were also more likely to have unsatisfactory restorations (OR = 2.28 95%CI: 1.05–4.92; p = 0.036). The prevalence of unsatisfactory restorations was high. The occurrence of this outcome was associated with restorative material, presence of caries, and visible plaque.